---- How did you know the surprising news?
---- I happened the event then.
A. to cover
B. to be covering
C. covering
D. to have covered
网友回答
A. to cover
(答案→)B. to be covering
C. covering
D. to have covered
解析：句意：--你怎么知道这个令人惊讶的消息的？--当时我碰巧在采访这个事件。Happen 后面一般接to do“碰巧要做”，因为当时正在采访，所以用happen to be doing碰巧正在做，选B。