---Was it the new school headmaster who walked by ?
--- .
A. It must be that
B. It must have been
C. He must be
D. This must have been
网友回答
A. It must be that
(答案→)B. It must have been
C. He must be
D. This must have been
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。