As he was about to go out to search for Mary, she happened .
A. to ing in
B. to e in
C. came in
D. to have e in
网友回答
A. to ing in
(答案→)B. to e in
C. came in
D. to have e in
解析：考查happen用法。Happen发生，碰巧；happen to do sth碰巧做某事；句意：当他正要出去找Mary的时候，她碰巧进来了。D项表示已经完成的事情，不符合句意。故Ｂ正确。