Luckily to be no one under the tree when it broke down.
A. it happened
B. there happened
C. there used
D. it had
网友回答
A. it happened
(答案→)B. there happened
C. there used
D. it had
解析：本题考查there be句型与happen to的连用，根据句意可知需要用there be结构，happen to表示“碰巧”。句意：幸运的，当树倒下的时候，下面碰巧没有人。