亲，求解答

xiaoyu612

Q40: It is theoretically possible that bacteriadeveloped on Mars early in its history and that some were carried to Earth by ameteorite.  However, strains of bacteriafrom different planets would probably have substantial differences in proteinstructure that would persist over time, and no two bacterial strains on Earthare different enough to have arisen on different planets.  So, even if bacteria did arrive on Earth fromMars, they must have died out. The argument is most vulnerable to which ofthe following criticisms? It fails to establish whether bacteria actually developed on     Mars. It fails to establish how likely it is that Martian bacteria     were transported to Earth. It fails to consider whether there were means other than     meteorites by which Martian bacteria could have been carried to Earth. It fails to consider whether all bacteria now on Earth could     have arisen from transported Martian bacteria. It fails to consider whether there could have been strains of     bacteria that originated on Earth and later died out.

kevingod

选D。
前提1.不同星球的菌落应该有很大区别。2.在地球上，没有哪两类菌落的区别大到可以判定他们来自于不同星球。

结论：即使有菌落之前从火星来到地球，他们也已经灭绝了（换句话说，目前地球上的菌落都是地球上土生土长的）

D weaken结论，地球上一开始没有菌落，这些菌落可以全部来自火星。这样也能满足两个前提，但是不支持结论。