GWD-6-40讨论帖仍不能使我满意

shzzhengfan

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.

考试时我会选D。但现在我对如何排除E有疑问。

前提：来自不同星球的细菌蛋白质结构会不同，地球上细菌的蛋白质结构相同。结论：即使有细菌来自火星，这些火星细菌也已死光了。

weaken：D：现在地球上所有细菌都来自火星。（即火星细菌没死光，直接反对结论）

E：有细菌曾产自地球，但这些地球细菌死光了（即，取非，地球细菌死光——现在细菌全是火星细菌，间接反对）

我的分析是，D，E只是直接和间接的区别，要问哪个most weaken，则选D。

大家的意见是？

shzzhengfan

不同意楼上的."no two bacterial strains on Earth are different enough" 只能说明现在地球上的细菌差别不大,至于细菌是哪的并没有暗示.

wycg

E是无关项.因为原文没提那些B是产自地球,后来die out了.

我觉得不能把E取非做无关推理.

AnyaAnya

就像楼主说的 有细菌曾产自地球，但这些地球细菌死光了 也不能说明是火星来的，也有可能是其他星球的，所以不能算是一个反对吧~

overthere33

E显然不对 题干没说火星是唯一的外来来源 地球上的死光了也不能说明现在剩下的是火星的 也可能火星的也死光了 现在剩下的是来自什么水星木星啥的呢

iflonely

我觉得E应该这样来理解：（见PREP2008解释）

首先楼主说的那个“间接”得出来自地球的细菌全死光，是不对的，因为这个选项与D不同，D那里有all说明了全部，而E那里没有all，即可以理解成部分，所以这里并不能说明“所有细菌都是来自于火星的”。

所以在这样的前提下，我们就不知道究竟剩下的是全部来自火星的，还是有一些是原来来自地球的（因为地球的没有完全灭绝），这样就无法解释“为什么蛋白质一样了”。