gwd6040

Q40:

It is theoretically possible that bacteria developed on Mars early in its history and that some were carried to Earth by a meteorite.  However, strains of bacteria from different planets would probably have substantial differences in protein structure that would persist over time, and no two bacterial strains on Earth are different enough to have arisen on different planets.  So, even if bacteria did arrive on Earth from Mars, they must have died out.

The argument is most vulnerable to which of the following criticisms?

1. It fails to establish whether bacteria actually developed on Mars.
2. It fails to establish how likely it is that Martian bacteria were transported to Earth.
3. It fails to consider whether there were means other than meteorites by which Martian bacteria could have been carried to Earth.
4. It fails to consider whether all bacteria now on Earth could have arisen from transported Martian bacteria.
5. It fails to consider whether there could have been strains of bacteria that originated on Earth and later died out.

答案是d

我选e

可能整个思路都不太对，请教大家！：）

The author assumes that bacteria from Mars is different from bacteria from Earth.Because all the bacterial strains on Earth are not significantly different,the bacterial strains must come from one source, the Earth. But what if the bacterial strains come from a different source,the Mars.This would weaken the author's conclusion.Therefore, D is the right answer.

E is irrelevant because whether some strains originated from earth and died out later is not relevant to the author's conclusion that even if bacteria did arrive on Earth from Mars, they must have died out.