牛人帮忙看下这个JJ 急求答案

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? 

A.      The gold content of the soil on Kodlunarn
                Island is much lower today than it was in the sixteenth century.

B.       The two mining expeditions funded by Elizabeth I did not mine the same part of Kodlunarn
                Island.
            

C.       The methods used to assess gold content of the soil samples provided by Frobisher were different from those generally used in the sixteenth century.
            

D.      Frobisher did not have soil samples from any other Canadian island examined for gold content.
            

E.       Gold was not added to the soil samples collected by Frobisher before the samples were examined.

答案是哪个啊