白勇语法51题 看不懂答案 求详解

sandychen168

各位大侠求解释啊 完全不知道为什么选C
Any medical test will sometimes fail to detect a condition when it is present and indicate that there is one when it is not.
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

-- by 会员 ychen34 (2011/12/31 9:28:51)

首先，detect是一个及物动词，要接宾语，所以可以排除BD。
然后E中it指代模糊，不知道指presence还是condition，放一边。
最后剩AC。AC的不同是indicate that 后面的那一部分。从未划线的when it is not可以看出，用it is present跟其平行。而不能用 there is one when it is not。因为，如果要用这个的话起码也是there is one when there is not这样。