单选题Passage Four The
biosphere is the name biologists give to the sort of skin on the surface of this
planet that is inhabitable by living organisms. Most land creatures occupy only
the interface between the atmosphere and the land; birds extend their range for
a few hundred feet into the atmosphere; burrowing invertebrates such as
earthworms may reach a few yards into the soil but rarely penetrate farther
unless it has been recently disturbed by men. Fish cover a wider range, from
just beneath the surface of the sea to those depths of greater than a mile
inhabited by specialized creatures. Fungi(真菌) and bacteria are plentiful in the
atmosphere to a height of about half a mile, blown there by winds from the lower
air. Balloon exploration of the stratosphere (同温层) as long ago as 1936 indicated
that moulds and bacteria could be found at heights of several miles, recently
the USA's National Aeronautics and Space Administration has detected them, in
decreasing numbers, at heights up to eighteen miles. They are pretty sparse at
such levels, about one for every two thousand cubic feet, compared with 50 to
100 per cubic foot at two to six miles (the usual altitude of jet aircraft), and
they are almost certainly in an inactive state. Marine bacteria have been
detected at the bottom of the deep Pacific trench, sometimes as deep as seven
miles; they are certainly not inactive. Living microbes have also been obtained
on land from cores of rock drilled (while prospecting for oil) at depths of as
much as 1,200 feet. Thus we can say, disregarding the exploits of astronauts,
that the biosphere has a maximum thickness of about twenty-five miles. Active
living processes occur only within a compass of about seven miles, in the sea,
on land and in the lower atmosphere, but the majority of living creatures live
within a zone of a hundred feet or so. If this planet were scaled down to the
size of an orange, the biosphere, at its extreme width, would occupy the
thickness of the orange-colored skin, excluding the pith. In
this tiny zone of our planet takes place the multitude of chemical and
biological activities that we call life. The way in which living creatures
interact with each other, depend on each other or compete with each other, has
fascinated thinkers since the beginning of recorded history. Living things exist
in a fine balance which is often taken for granted—for, from a practical point
of view, things could not be otherwise. Yet it is a source of continual
amazement to scientists because of its intricacy and delicacy. The balance of
nature is obvious most often when it is disturbed, yet even here it can seem
remarkable how quickly it readjusts itself to a new balance after a disturbance.
The science of ecology—the study of the interaction of organisms with their
environment—has grown up to deal with the minutiae of the balance of
nature.
单选题
According to the passage, the "biosphere" is the layer on earth's
surface ______.
A. where the atmosphere meets the sea
B. in which birds, fish and animals would die
C. in which plant and animal life can exist
D. in which earthworms and other invertebrates can live
【正确答案】
C
【答案解析】“The biosphere is…this planet that is inhabitable by living organisms．”表明“生物圈指地球上生物可生存的表层”，所以选C。
单选题
The writer states that fungi and bacteria ______.
A. are only found below the normal altitude of jet planes
B. have been found well at the normal altitude of jet planes
C. are not found below the surface of the earth
D. are mainly found below the surface of the earth