4.(Z4)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?
A. It fails to establish whether bacteria actually developed on Mars.
B. It fails to establish how likely it is that Martian bacteria were transported to Earth.
C. It fails to consider whether there were means other than meteorites by which Martian bacteria could have been carried to Earth.
D. It fails to consider whether all bacteria now on Earth could have arisen from transported Martian bacteria.
E. It fails to consider whether there could have been strains of bacteria that originated on Earth and later died out.
请帮忙解释一下
哪位高人能指点一下阿~~~~急急急
原文大意：
科学家认为，目前一些地球上的细菌可能来自于火星。
然而，来自火星的细菌应该在构造上与地球上的不同，（而且，这种不同不会因为时间而改变）
但是，现在地球上的细菌，在构造上没有明显不同。
所以，地球上的细菌不可能来自火星，（即使来自火星也早就完蛋了）。
这里的关键是：地球上的细菌没有明显的构造之不同。这种不同可能导致两种结论：
1。如结论所说，现在的细菌都是土生土长在地球上的；
2。如D所说，全部来自火星。
因此，既然前提可以导出两个结论，那么很明显，第二个结论作者没有考虑进去，也就是flaw的所在。
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