GMAT-5-40请教求解思路

sv2000

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?

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yangsh

D,

sv2000

能解释一下吗？谢谢

carolhide

不同星球上的细菌的蛋白质结构有显著差别+地球上细菌的蛋白质结构都相同=>从火星来的细菌已经死绝了。

地球上细菌的蛋白质结构相同说明细菌来自同个星球，可以是地球自己的，也可以是火星的。