---Was it the new school headmaster who walked by ?
--- _____A.It must be thatB.It must have beenC.He must beD.This must have been
网友回答
B解析考查问题回答，问句是it为主语，回答也是it为主语，而且是对过去情况的推测，选B，句意是：--刚刚走过的是校长吗？--一定是。It must have been =It must have been the new school headmaster。