----- 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：考查不定式用法。固定词组happen to do sth碰巧做某事；如果后面的动作是已经发生的，就使用不定式的完成式；如果动作是与谓语动词同时发生的，就用不定式的进行式。句意：—你是怎么知道这个出人意料的消息的？—那个时候我碰巧正在采访那个事情。故B正确。