(A) crash, but they have also ignored demands by the pilots union that the investigation should be expedited

(B) crash but also ignored demands by the pilots union that the investigation be expedited

(C) crash but have ignored demands for expediting the investigation by the pilots’ union

(D) crash, but they are also ignoring the pilots’ union’s demands to expedite the investigation（B） (E) crash: the demands by the pilots’ union that the investigation should be expedited have also been ignored 问题是为什么C选项中，but also 前面没有逗号？

是B的but also吧。

but also在引导independant的句子的时候前面才要加逗号。也就是说，当but also后有主+谓结构时才要“,”

这是我个人做题的感觉，希望其他NN指正