My pain ___________ obvious the moment I walked into the room, for the first man I met asked me pitifully: Are you feeling all right?
A.must be
B.must have been
C.could be
D.could have been
网友回答
B解析本题是情态动词的考查。根据后半个分句可以知道谓语动词发生于过去，而情态动词+动词的完成式表示对过去的推测。