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?

1. The gold content of the soil on Kodlunarn
    Island is much lower today than it was in the sixteenth century.
2. The two mining expeditions funded by Elizabeth I did not mine the same part of Kodlunarn
     Island.
3. The methods used to assess gold content of the soil samples provided by Frobisher were different from those generally used in the sixteenth century.
4. Frobisher did not have soil samples from any other Canadian island examined for gold content.
5. Gold was not added to the soil samples collected by Frobisher before the samples were examined.

答案是E，我选的D，请n人指教，谢谢.

PS：E选项说没有在样本里加入gold，本来就是样本怎么还有人会往里面加入东西呢？不是很荒唐么？