SC-3

qiufeng1990

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

B) the presence of a condition when it is there and indicate its presence.

Why B is wrong?

andrewcan

"the presence of a condition indicate its presence" is unidiomatic.

tongxun

主要是indicate its presence when it is not.中的it 指带不明。在他的前面有一名词presence，若它前面有it，就指带it，但现在没有，根据就近指带的原则，指带presence。而从逻辑上讲，it 应该指带condition的。