Câu 50. A. what B. why C. how D. where
Đọc kĩ đoạn văn sau và chọn phương án đúng án đúng (A,B,C hoặc D)cho mỗi câu.
According to the best evidence gathered by space probes and astronomers, Mars is an inhospitable planet, more
similar to Earth’s Moon than to Earth it self – a dry , stark , seemingly lifeless world. Mars’ air pressure is equal to
Earth’s at an altitude of 100,000 feet. The air there is 95 percent carbon dioxide.
Mars has no ozone layer to screen out the sun’s lethal radiation.Daytime temperatures may reach above freezing,
but because the planet is blanketed by the mere wisp of an atmostphere, the heat radiates back into space . Even at
the equator, the temperature drops to -50C ( -60F ) at night.Today there is no liquid water, although valleys and
chnnels on the surface show evidence of having been carved by running water. The polar ice caps are made of
frozen water and carbon dioxide , and water may be frozen in the ground as permafrost.
Despite these difficult conditions, certain scientists believe that there is a possibility of trans-forming Mars into a
more Earth-like planet. Nuclear reactors might be used to melt frozen gases and eventually build up the atmostphere.
This in turn could create a “ greenhouse effect ” that would stop heat from radiating back into space. Liquid water
could be thawed to from a polar ocean. Once enough ice has melted, suitable plants could be introduced to build up
the level of oxygen in the atmostphere so that, in time, the planet would support animal life from Earth and even
permanent human colonies. “ This was once thought to be so far in the future as to be irrelevant,” said Christopher
Mckay, a research scientist at NASA . “ But now it’s starting to look practical. We could begin word in four or five
decades.”
The idea of “ terra-forming” Mars, as enthusiasts call it, has its roots in science fiction. But as researchers develop
a more profound understanding of how Earth's ecology supports life, they have begun to see how it may be pssible
to create similar conditions on Mars. Don’t plan on homesteading on Mars any time soon, though. The process could
take hundreds or even thousands of years to complete and the cost would be staggering.
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