阅读理解The word "it" in line 24 refers to
阅读理解Artisans and Industrialization
Before 1815 manufacturing in the United States had been done in homes or shops by skilled artisans
阅读理解Geographers say that what defines a place are four properties: soil, climate, altitude,
and aspect, or attitude to the Sun. Florida''s ancient scrub demonstrates this principle. Its
soil is pure silica, so barren it supports only lichens as ground cover.(It does, however,
sustain a sand-swimming lizard that cannot live where there is moisture or plant matter
(5) the soil.) Its climate, despite more than 50 inches of annual rainfall, is blistering desert
plant life it can sustain is only the xerophytic, the quintessentially dry. Its altitude is a
mere couple of hundred feet, but it is high ground on a peninsula elsewhere close to sea
level, and its drainage is so critical that a difference of inches in elevation can bring major
changes in its plant communities. Its aspect is flat, direct, brutal―and subtropical.
(10) Florida''s surrounding lushness cannot impinge on its ''desert scrubbiness.
This does not sound like an attractive place. It does not look much like one either;
Shrubby little oaks, clumps of scraggly bushes, prickly pear, thorns, and tangles. "It appear
Said one early naturalist," to desire to display the result of the misery through which it has
Passed and is passing." By our narrow standards, scrub is not beautiful; neither does it meet
(15) our selfish utilitarian needs. Even the name is an epithet, a synonym for the stunted, the
scruffy, the insignificant, what is beautiful about such a place?
The most important remaining patches of scrub lie along the Lake Wales Ridge, a chain
of paleoislands running for a hundred miles down the center of Florida, in most places less
than ten miles wide. R is relict seashore, tossed up millions of years ago when ocean levels
(20) were higher and the rest of the peninsula was submerged. That ancient emergence is
precisely what makes Lake Wales Ridge so precious: it has remained unsubmerged , its
ecosystems essentially undisturbed, since the Miocene era. As a result, it has gathered to
itself one of the largest collections of rare organisms in the world. Only about 75 plant
species survive there, but at least 30 Of these are found nowhere else on Earth.
阅读理解Both in what is now the eastern and the southwestern United States, the peoples of
the Archaic era (8,000-1,000 B.C) were, in a way, already adapted to beginnings of
cultivation through their intensive gathering and processing of wild plant foods. In both
areas, there was a well-established ground stone tool technology, a method of pounding
(5) and grinding nuts and other plant foods, that could be adapted to newly cultivated foods.
By the end of the Archaic era, people in eastern North America had domesticated certain
native plants, including sunflowers; weeds called goosefoot, sumpweed, or marsh elder;
and squash or gourds of some kind. These provided seeds that were important sources of
carbohydrates and fat in the diet.
(10) The earliest cultivation seems to have taken place along the river valleys of the
Midwest and the Southeast, with experimentation beginning as early as 7,000 years ago
and domestication beginning 4,000 to 2,000 years ago. Although the term “Neolithic” is
not used in North American prehistory, these were the first steps toward the same major
subsistence changes that took place during the Neolithic (8,000-2,000 B.C.) period
(15) elsewhere in the world.
Archaeologists debate the reasons for beginning cultivation in the eastern part of the
continent. Although population and sedentary living were increasing at the time, there is
little evidence that people lacked adequate wild food resources; the newly domesticated
foods supplemented a continuing mixed subsistence of hunting, fishing, and gathering
(20) wild plants, Increasing predictability of food supplies may have been a motive. It has
been suggested that some early cultivation was for medicinal and ceremonial plants rather than
for food. One archaeologist has pointed out that the early domesticated plants were all
weedy species that do well in open, disturbed habitats, the kind that would form around
human settlements where people cut down trees, trample the ground, deposit trash, and
(25) dig holes. It has been suggested that sunflower, sumpweed, and other plants almost
domesticated themselves, that is , they thrived in human –disturbed habitats, so humans
intensively collected them and began to control their distribution. Women in the Archaic
communities were probably the main experimenters with cultivation, because
ethnoarchaeological evidence tells us that women were the main collectors of plant food
and had detailed knowledge of plants.
阅读理解A survey is a study, generally in the form of an interview or a questionnaire, that provides
information concerning how people think and act. In the United States, the best-known
surveys are the Gallup poll and the Harris poll. As anyone who watches the news during Line
campaigns presidential knows, these polls have become an important part of political life in
(5) the United States.
North Americans are familiar with the many "person on the street? interviews on local
television news shows. While such interviews can be highly entertaining, they are not
necessarily an accurate indication of public opinion. First, they reflect the opinions of only
those people who appear at a certain location. Thus, such samples can be biased in favor
(10)of commuters, middle-class shoppers, or factory workers, depending On which area the
newspeople select. Second, television interviews tend to attract outgoing people who are
willing to appear on the air, while they frighten away others who may feel intimidated by
a camera. A survey must be based on a precise, representative sampling if it is to genuinely
reflect a broad range of the population.
(15) In preparing to conduct a survey, sociologists must exercise great care in the wording
of questions. An effective survey question must be simple and clear enough for people to
understand it. It must also be specific enough so that there are no problems in interpreting
the results. Even questions that are less structured must be carefully phrased in order to elicit
the type of information desired. Surveys can be indispensable sources of information, but
(20)only if the sampling is done properly and the questions are worded accurately.
There are two main forms of surveys: the interview and the questionnaire. Each of these
forms of survey research has its advantages. An interviewer can obtain a high response rate
because people find it more difficult to turn down a personal request for an interview than
to throw away a written questionnaire. In addition, an interviewer can go beyond written
(25)questions and probe for a subject''s underlying feelings and reasons. However, questionnaires
have the advantage of being cheaper and more consistent.
阅读理解Green Icebergs
Icebergs are massive blocks of ice, irregular in shape; they float with only about 12 percent of their mass above the sea surface
阅读理解Infantile Amnesia
What do you remember about your life before you were three? Few people can remember anything that happened to them in their early years
阅读理解The Origins of Cetaceans
It should be obvious that cetaceans-whales, porpoises, and dolphins-are mammals
阅读理解Perhaps one of the most dramatic and important changes that took place in the
Mesozoic era occurred late in that era, among the small organisms that populate the
uppermost, sunlit portion of the oceans--the plankton. The term "plankton" is a broad
one, designating all of the small plants and animals that float about or weakly propel
(5) themselves through the sea. In the late stages of the Mesozoic era. during the Cretaceous
period, there was a great expansion of plankton that precipitated skeletons or shells
composed of two types of mineral: silica and calcium carbonate. This development
radically changed the types of sediments that accumulated on the seafloor, because,
while the organic parts of the plankton decayed after the organisms died, their mineralized
(10)skeletons often survived and sank to the bottom. For the first time in the Earth''s long
history, very large quantities of silica skeletons, which would eventually harden into rock,
began to pile up in parts of the deep sea. Thick deposits of calcareous ooze made up of
the tiny remains of the calcium carbonate-secreting plankton also accumulated as never
before. The famous white chalk cliffs of Dover, in the southeast of England, are just one
(15)example of the huge quantities of such material that amassed during the Cretaceous
period; there are many more. Just why the calcareous plankton were so prolific during
the latter part of the Cretaceous period is not fully understood. Such massive amounts
of chalky sediments have never since been deposited over a comparable period of time.
The high biological productivity of the Cretaceous oceans also led to ideal conditions
(20)for oil accumulation. Oil is formed when organic material trapped in sediments is slowly
buried and subjected to increased temperatures and pressures, transforming it into
petroleum. Sediments rich in organic material accumulated along the margins of the
Tethys Seaway, the tropical east-west ocean that formed when Earth''s single landmass
(known as Pangaea) split apart during the Mesozoic era. Many of today''s important oil
(25)fields are found in those sediments--in Russia, the Middle East, the Gulf of Mexico, and
in the states of Texas and Louisiana in the United States.
阅读理解Why does the author mention the first Baedeker Travel Guide to the United States?
阅读理解If food is allowed to stand for some time, it putrefies .When the putrefied material
is examined microscopically ,it is found to be teeming with bacteria. Where do these
bacteria come from, since they are not seen in fresh food? Even until the mid-nineteenth
century, many people believed that such microorganisms originated by spontaneous
(5) generation ,a hypothetical process by which living organisms develop from nonliving matter.
The most powerful opponent of the theory of spontaneous generation was the French chemist
and microbiologist Louis Pasteur(1822-1895).Pasteur showed that structures
present in air closely resemble the microorganisms seen in putrefying materials .He did
(10)this by passing air through guncotton filters, the fibers of which stop solid particles. After
the guncotton was dissolved in a mixture of alcohol and ether, the particles that it had
trapped fell to the bottom of the liquid and were examined on a microscope slide .Pasteur
found that in ordinary air these exists a variety of solid structures ranging in size from
0.01 mm to more than 1.0 mm .Many of these bodies resembled the reproductive
(15)structures of common molds, single-celled animals, and various other microbial cells.
As many as 20 to 30 of them were found in fifteen liters of ordinary air ,and they could
not be distinguished from the organisms found in much larger numbers in putrefying
materials .Pasteur concluded that the organisms found in putrefying materials originated
from the organized bodies present in the air .He postulated that these bodies are constantly
(20)being deposited on all objects.
Pasteur showed that if a nutrient solution was sealed in a glass flask and heated to
boiling to destroy all the living organisms contaminating it, it never putrefied .The proponents of
spontaneous generation declared that fresh air was necessary for
spontaneous generation and that the air inside the sealed flask was affected in some way
(25)by heating so that it would no longer support spontaneous generation. Pasteur constructed a
swan-necked flask in which putrefying materials could he heated to boiling, but air
could reenter. The bends in the neck prevented microorganisms from getting in the flask.. Material
sterilized in such a flask did not putrefy.
阅读理解Nineteenth-Century Politics in the United States
The development of the modern presidency in the United States began with Andrew Jackson who swept to power in 1829 at the head of the Democratic Party and served until 1837
阅读理解Petroleum Resources
Petroleum, consisting of crude oil and natural gas, seems to originate from organic matter in marine sediment
阅读理解The Moon, which has undergone a distinct and complex geological history, presents a
striking appearance. The moon may be divided into two major terrains: the maria (dark
lowlands) and the terrace( bright highlands). The contrast in the reflectivity (the capability
of reflecting light) of these two terrains suggested to many early observers that the two
(5) terrains might have different compositions, and this supposition was confirmed by missions to
the Moon such as Surveyor and Apollo. One of the most obvious differences
between the terrains is the smoothness of the maria in contrast to the roughness of the
highlands. This roughness is mostly caused by the abundance of craters; the highlands are
completely covered by large craters(greater than 40-50 km in diameter), while the craters
(10) of the maria tend to be much smaller. It is now known that the vast majority of the Moon''s
craters were formed by the impact of solid bodies with the lunar surface.
Most of the near side of the Moon was thoroughly mapped and studied from telescopic
pictures years before the age of space exploration. Earth-based telescopes can resolve
objects as small as a few hundred meters on the lunar surface. Close observation of
(15) craters, combined with the way the Moon diffusely reflects sunlight, led to the
understanding that the Moon is covered by a surface layer, or regolith, that overlies the
solid rock of the Moon. Telescopic images permitted the cataloging of a bewildering array
of land forms. Craters were studied for clues to their origin; the large circular maria were
(20) seen. Strange, sinuous features were observed in the maria. Although various land forms
were catalogued, the majority of astronomers'' attention was fixed on craters and their
origins.
Astronomers have known for a fairly long time that the shape of craters changes as
they increase in size. Small craters with diameters of less than 10-15 km have relatively
(25) simple shapes. They have rim crests that are elevated above the surrounding terrain,
smooth, bowl-shaped interiors, and depths that are about one-fifth to one-sixth their diameters.
The complexity of shape increases for larger craters.
阅读理解The smooth operation of an ant colony depends on ten to twenty different signals,
most of which are pheromones (chemical signals triggering behavioral responses). It is
estimated that red fire ants employ at least twelve different chemical signals. The simples
of these is the carbon dioxide from the respiration of an ant cluster, a chemical that acts
(5) a pheromone to promote aggregation. Workers move toward a source of carbon dioxide,
resulting in solitary ants moving to join a group. At the other extreme, the most complex
of the fire ants'' signals is probably colony odor, by which the workers of a particular
colony or nest identify another worker as local or foreign. Each ant nest has its own odor
as a result of its location, history, and local food supply. The resident ants pick up this
(10) odor on their bodies, so that ants of the same species, but from different nests, have
different colony odors. This allows ants to identify intruders and maintain colony
integrity.
Fire ants also make use of an alarm pheromone to alert workers to an emergency,
and their scouts lay down a trail pheromone as a guide during mass migrations. A fire ant
(15) queen emits a chemical signal that identifies her to the colony''s workers. They respond
by scurrying to gather around her. The decomposing corpse of a dead ant also generates
a signal, to which workers respond by eliminating the corpse from the nest.
Ants provide examples of both public (accessible to other species) and private
messages. One of their most important private messages concerns food, for a food source
(20) is worth keeping secret. Each species marks its trails with signals that are meaningless to
others, so that an ant crossing a trail left by another ant species typically notices nothing.
On the other hand, a secret signal to mark a dead body is unnecessary. Many kinds of ants
perceive a natural decomposition product of dead insects as a signal to remove a corpse.
If an outsider recognizes this message and moves the body, no harm is done.
阅读理解Lascaux Cave Paintings
In Southwest France in the 1940s, playing children discovered Lascaux Grotto, a series of narrow cave chambers that contain huge prehistoric paintings of animals
阅读理解The Cambrian Explosion
The geologic timescale is marked by significant geologic and biological events, including the origin of Earth about 4
阅读理解The Geologic History of the Mediterranean
In 1970 geologists Kenneth J
阅读理解According to the passage, factory workers differed from craft workers in that factoryworkers
阅读理解Agriculture, Iron, and the Bantu Peoples
There is evidence of agriculture in Africa prior to 3000 B