关于ASSUMPTION削弱取反的问题

lainemai

我做ASSUMPTION题经常就是用削弱取反的方法来做的，但是最近做了几道题错后发现，其实取反并不能削弱结论于是我就纳闷了，比如这道GWD上的：

Frobisher, a sixteenth-century English explorer, had soil samples from Canada's Kodlunarn Island examined for gold content. Because high gold content was reported, Elizabeth I funded two mining expeditions. Neither expedition found any gold there. Modern analysis of the island's soil indicates a very low gold content. Thus the methods used to determine the gold content of Frobisher's samples must have been inaccurate.

Which of the following is an assumption on which the argument depends?

• AThe gold content of the soil on Kodlunarn Island is much lower today than it was in the sixteenth century.  
• BThe two mining expeditions funded by Elizabeth I did not mine the same part of Kodlunarn Island.  
• CThe methods used to assess gold content of the soil samples provided by Frobisher were different from those generally used in the sixteenth century.  
• DFrobisher did not have soil samples from any other Canadian island examined for gold content.  
• EGold was not added to the soil samples collected by Frobisher before the samples were examined.  
• 正确答案是E，我选的是B，我当时做题的时候确实看过答案E，并且将它取反，就是GOLD WAS ADDED TO THE SOIL SAMPLES COLLECTED BY F BEFORE THE SAMPLES WERE EXAMINED.
• 这样子的话，就是说F在检测soil之前就已经加了金子进去，那么确实会造成测量结果不准确，并没有削弱结论的意思呀，求大神解释~~