OG83

Any medical test will sometimes fail to detect a condition when it is present and indicate that there is one when it is not.

(A) a condition when it is present and indicate that there is one

(B) when a condition is present and indicate that there is one

(C) a condition when it is present and indicate that it is present

(D) when a condition is present and indicate its presence

(E) the presence of a condition when it is there and indicate

我对one的用法有疑问，它也有代词的用法，为什么ets说，用了one之后it就指代不明了？

以下是tianwan牛牛的解释   

C,全句用同样的代词it几次，这些代词it都指代condition，没有争议。

AB的最后一个it可能指向one和condition，引起争议；one是替代，it是指代，it和one都指向condition，用2个代词指向同一对象不对。

我想知道一句话中两个代词不能同一事物吗？有这样的规定吗？

http://forum.chasedream.com/dispbbs.asp?boardID=23&ID=27472&page=1

我想知道一句话中两个代词不能同一事物吗？有这样的规定吗？

-- It depends.

   如两个 it 可以指代同一事物。但，如果代词是it 和 they，就不能指代同一事物了。