贾岛简介20字:只能依靠你

D

如果是B的话,好像少了一个介词 IN

虚拟语气，选b，d是未来完成时态
if only 开头，位于结构倒装，然后后面一句话正好是表示的假设的情况，并没有实现，所以是虚拟语气，如此看来，b正好表示对过去的虚拟。

应该选B，准没错。

选b
意思是，如果她通过了考试，就有资格来担任这个职务的。
虚拟语气。假如没有考试失败的话。而d体现不出来。

A =

For A to work we have to change the tense of the rest of the sentence

If only she will take the exam, she could qualify for the position.

B =

If only she hadn't failed the exam, she could have been qualified for the position.

To qualify for the position she needed to pass that exam.

C =

She has failed the exam so she can't qualify for the position.

D =

If only she would have taken the exam, she COULD have been qualified for the position.

If she takes the exam she might not pass it, so just taking the exam doesn't automatically qualify her for the position.

To suggest MAYBE she would have qualified we could use "could" which is less certain than "would"

so B is correct.