单选题Diseases of Agricultural Plants Plants, like animals, are subject to diseases of various kinds. It has been estimated that some 30,000 different diseases attack our economic plants; forty are known to attack corn, and about as many attack wheat. The results of unchecked plant disease are all too obvious m countries which have marginal food supplies. The problem will soon be more widespread as the population of the world increases at its frightening rate. Even in countries which are now amply fed by their agricultural products there could soon be critical food shortages. It is easy to imagine the consequences of some disastrous attack on one of the major crops; the resulting famines could kill millions of people, and the resulting hardship on other millions could cause political upheavals disastrous to the order of the world. Some plants have relative immunity to a great many diseases, while others have a susceptibility to them. The tolerance of a particular plant changes as the growing conditions change. A blight may be but a local infection easily controlled; on the other hand it can attack particular plants in a whole region or nation. An example is the blight which killed virtually every chestnut tree in North America. Another is the famous potato blight in Ireland in the last century. As a result of that, it was estimated that one million people died of starvation and related ailments. Plant pathologists have made remarkable strides in identifying the pathogens of the various diseases. Bacteria may invade a plant through an infestation of insect parasites carrying the pathogen. A plant can also be inoculated by man. Other diseases might be caused by fungus which attacks the plant in the form of a mold or smut or rust. Frequently such a primary infection will weaken the plant so that a secondary infection may result from its lack of tolerance. The symptoms shown may cause an error in diagnosis, so that treatment may be directed toward bacteria which could be the result of a susceptibility caused by a primary virus infection.
单选题Colds are very common. The symptoms of the common cold include a sore throat, runny nose, stuffed-up nose, and tiredness. Colds are caused by viruses, but scientists cannot explain the exact cause. There is no cure. Many people, however, believe that they know the causes of and cures for the common cold. For example, they believe that it is possible to get a cold if we get chilled, if we get extra tired, or if we are too close to a person with a cold. In other words, if we want to prevent catching cold, we should stay warm and dry; we should avoid getting too tired, and we should not be in close contact with people who have colds. Meanwhile, there are probably hundreds of " cures" throughout the world for the common cold. For example, the following suggestions are popular in quite a number of societies : (1) drink plenty of water; (2) get extra rest; (3) take a lot of vitamin C; (4) take aspirin; (5) keep warm. Each year people spend a lot of money on cold medicines-pills, liquids, lozenges (含片). But these medicines do not cure colds; they can only relieve cold symptoms. In other words, they make us feel better.
单选题The Moon and most artificial satellites travel around the Earth in elliptical paths.A. wavesB. orbitsC. voyagesD. flights
单选题
下面有3篇短文,每篇短文后有5道题,每题后面有4个选项。请仔细阅读短文并根据短文回答其后面的问题。{{B}}第一篇{{/B}}
{{B}}
The English Weather{{/B}} "Other
countries have a climate; in England we have weather". This statement, often
made by Englishmen to describe the strange weather conditions of their country,
is both revealing and true. It is revealing because in it we see the Englishman
insisting once again that what happens in England is not the same as what
happens elsewhere. Its truth can be proved by any foreigner who stays in the
country for longer than a few days. In no country other than
England, it has been said, can one experience four seasons in the course of a
single day! Day may break as a warm spring morning; an hour or so later black
clouds may have appeared from nowhere and the rain may be pouring down. At
midday it may be really winter with the temperature down by about eight degrees
or more centigrade(摄氏度 ). And then, in the late afternoon the sky will clear,
the sun will begin to shine, and for an hour or two before darkness fails, it
will be summer. In England one can experience almost every kind
of weather except the most extreme. (Some foreigners seem to be under the
impression that for ten months of the year the country is covered by a dense
blanket of fog; this is not true.)The problem is that we never can be sure when
the different types of weather will occur. Not only do we get several different
sorts of weather in one day, but we may very well get a spell(持续的一段时间) of winter
in summer and a spell of summer in winter. The uncertainty about
the weather has had a definite effect upon the Englishman's character. It tends
to make him cautious(小心谨慎的),for example. The foreigner may laugh when he sees
the Englishman setting forth on a brilliantly sunny morning wearing a raincoat
and carrying an umbrella, but he may well regret his laughter later in the
day! And, of course, the weather's variety provides a constant
topic of conversation. Even the most taciturn (沉默寡言的) of Englishmen is always
prepared to discuss the weather. And, though he sometimes complains bitterly of
it, he would not, even if he could, exchange it for the more predictable climate
of other lands.
单选题A small number of
firms
have stopped trading.
单选题It is
laid down
in the regulations that all members must carry their membership cards at all times.
单选题After making observations for a week in the plant, the industrial engineer made a number of very {{U}}constructive{{/U}} suggestions in an oral report to the manager.
单选题If a company is paying Jersey or Guernsey income tax, the Authorities will require the filing of amounts to {{U}}substantiate{{/U}} the assessable profit.
单选题As a result of careless washing the jacket was reduced to a child's size~
单选题U.S. to Start $3.2 Billion Child Health Study in January
A study that will cost $3.2 billion and last more than two decades to track the health of 100,000 U.S. children from before birth to age 21 will be launched in January, U.S. health officials said on Friday.
Officials from the U.S. government"s National Institutes of Health (NIH) said they hope the study, to be conducted at 105 locations throughout the United States, can help identify early-life influences that affect later development, with the goal of learning new ways to treat or prevent illness.
The study will examine hereditary and environmental factors such as exposure to certain chemicals that affect health.
Researchers will collect genetic and biological samples from people in the study as well as samples from the homes of the women and their babies including air, water, dust and materials used to construct their residences, the NIH said.
Officials said more than $200 million has been spent already and the study is projected to cost $3.2 billion.
"We anticipate that in the long term, what we learn from the study will result in a significant savings in the nation"s health care costs," Dr. Duane Alexander, who heads the NIH"s Eunice Kennedy Shriver National Institute of Child Health and Human Development, told reporters.
The study will begin in January when the University of North Carolina and the Mount Sinai School of Medicine in New York start signing up pregnant women whose babies will then be followed to age 21.
Some of the early findings will be about factors behind pre-term birth, which has become more common in recent years, according to Dr. Peter Scheidt of the NIH, who heads the study.
The people taking part will be from rural, urban and suburban areas, from all income and educational levels and from all racial groups, the NIH said.
单选题You can {{U}}turn to{{/U}} different kinds of people, dictionaries or maps, to find out what you wish to know.
单选题Most people find
rejection
hard to accept.
单选题One Good Reason to Let Smallpox Live It's now a fair bet that we will never see the total extinction of the smallpox virus. The idea was to cap the glorious achievement of 1980, when smallpox was eradicated in the wild, by destroying the killer virus in the last two labs that are supposed to have it-one in the US and one in Russia. If smallpox had truly gone from the planet, what point was there in keeping these reserves? (51) reality, of course, it was naive to (52) that everyone would let (53) of such a potent potential weapon. 1 Undoubtedly several nations still have (54) vials. (55) the last "official" stocks of live virus bred mistrust of the US and Russia, (56) no obvious gain. Now American researchers have (57) an animal model of the human disease, opening the (58) for tests on new treatments and vaccines. So one again there's a good reason to (59) the virus-just in (60) the disease puts in a reappearance. How do we (61) with the mistrust of the US and Russia? (62) Keep the virus (63) international auspices in a well-guarded UN laboratory that's open to all countries. The US will object, of course, just as it rejects a multilateral approach to just about everything. But it doesn't (64) the idea is wrong. If the virus (65) useful, the let's make it the servant of all humanity—not just a part of it.
单选题The number of college student is on rise recently.A. increasingB. droppingC. decreasingD. reducing
单选题Congressional debate over the passage of this controversial bill is inevitable.A. popularB. personalC. disputedD. beneficial
单选题When Cousins wrote his book, everyone agreed with him.
单选题 阅读下面的短文,文中有15处空白,每处空白给出了4个选项,请根据短文的内容从4个选项中选择1个最佳答案。
{{B}}Diet,
Alcohol Linked to Nearly One Third of Cancers{{/B}} Diet is second
only to tobacco as a leading{{U}} (51) {{/U}}of cancer and, along with
alcohol, is responsible for nearly one third of cases of the disease{{U}}
(52) {{/U}}developed countries, a leading researcher said on
Tuesday. Dr. Tim Key, of the University of Oxford, told a cancer
conference that scientists are still discovering how certain foods contribute
to{{U}} (53) {{/U}}, but they know that diet, alcohol and obesity{{U}}
(54) {{/U}}a major role. "Five percent of cancers
could be avoided{{U}} (55) {{/U}}nobody was obese," he said.
While tobacco is linked to about 30{{U}} (56) {{/U}}of cancer
cases, diet is involved in an estimated 25 percent and alcohol{{U}} (57)
{{/U}}about six percent. Obesity raises the{{U}} (58)
{{/U}}of breast, womb, bowel and kidney cancer, while alcohol is known to
cause cancers of the mouth, throat and liver. Its dangerous impact is{{U}}
(59) {{/U}}when combined with smoking. Key told the
meeting of the charity Cancer Research UK{{U}} (60) {{/U}}other elements
of diet linked to cancer are{{U}} (61) {{/U}}unknown but scientists are
hoping that the EPIC study, which is comparing the diets Of 500,000 people in 10
countries and their risk of cancer, will provide some{{U}} (62)
{{/U}}. Early results of the study have revealed that
Norway, Sweden and Denmark have the{{U}} (63) {{/U}}consumption of fruit
and vegetables among European countries while Italy and Spain have the highest.
Eating at{{U}} (64) {{/U}}five portions of fruit and vegetables a day is
recommended to reduce the risk of cancer. Key, principal
scientist on the EPIC study, said it is looking at dietary links to some of the
most common cancers{{U}} (65) {{/U}}colorectal, breast and
prostate.
单选题A turbulent storm was a major factor in the defeat of the Spanish Armada.A. noxiousB. violentC. mysteriousD. pathetic
单选题The U.S. faces
severe
economic problems.
单选题What were the effects of the decision she made?