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Q5 to Q7:
In 1994, a team of scientists led
by David Mckay began studying the
meteorite ALH84001, which had been
Line discovered in LACE>AntarcticaLACE> in 1984.
(5) Two years later, the McKay team
announced that ALH84001, which
scientists generally agree originated
on Mars, contained compelling evi-
dence that life once existed on Mars.
(10) This evidence includes the discovery
of organic molecules in ALH84001,
the first ever found in Martian rock.
Organic molecules—complex, carbon-
based compounds—form the basis for
(15) terrestrial life. The organic molecules
found in ALH84001 are polycyclic aro-
matic hydrocarbons, or PAH’s. When
microbes die, their organic material
often decays into PAH’s.
(20) Skepticism about the McKay team’s
claim remains, however. For example,
ALH84001 has been on earth for
13,000 years, suggesting to some
scientists that its PAH’s might have
(25) resulted form terrestrial contamination.
However, McKay’s team has demon-
strated that the concentration of PAH’s
increases as one looks deeper into
ALH84001, contrary to what one would
(30) expect from terrestrial contamination.
The skeptic’s strongest argument,
however, is that processes unrelated
to organic life can easily produce all
the evidence found by McKay’ steam,
(35) including PAH’s. For example, star
formation produces PAH’s. Moreover,
PAH’s frequently appear in other
meteorites, and no one attributes
their presence to life processes.
(40) Yet McKay’s team notes that the
particular combination of PAH’s
in ALH84001 is more similar to the
combinations produced by decaying
organisms than to those originating
form nonbiological processes.
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Q5:E
The passage asserts which of the following about the claim that ALH84001 originated on Mars?
- It was initially proposed by the McKay team of scientists.
- It is not a matter of widespread scientific dispute.
- It has been questioned by some skeptics of the McKay team’s work.
- It has been undermined by recent work on PAH’s.
- It is incompatible with the face that ALH84001 has been on Earth for 13,000 years.
KEY: B, 为什么D不对？谢谢 | 
