OG 83题

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 its presence

我对答案没有异议，可是OG的解释说正确答案C里的it指代清楚，我的问题是难道这里it没有可能指代any medical test吗？恳请牛牛指点。

第一个it的指代，我觉得这里when从句在主句之后，it可能更倾向于先指前面的名词a condition ，而不是指对应主句的主语Any medical test 。如果是when it is present，any medical test will sometimes fail to detect a condition 。这里it应该先对应any medical test 。我想起一题because they，主语........和主语.....because they除了because的位置其它都一样，主句中可能有其它复数名词。此题意思明显是they指代主语，最后的答案是前者。

剩下的it跟前it一致不会有问题。

当然问题应该不会那么简单。我想做题时主要还是一靠比较，二看意思来分辨指代的合理性。