It is by no means clear _____ the president can do to end the st

It is by no means clear _____ the president can do to end the strike.
A、how
B、which
C、that
D、what
【正确答案】：D
【题目解析】：此处it是形式主语，what引导的是主语从句，作真正的主语。What作do的宾语。句意：总统采取什么行动结束这次罢工一点也不清楚。【考点】考查主语从句的连接词。