题目内容
完成句子
I _________(看见)her getting on the bus when I came out of the bookstore．
我看见他在擦黑板。
I saw him ________(clean)the blackboard．
我看见他擦了黑板。
I saw him _________(clean)the blackboard．
我看见这封信纯属偶然。
I saw the letter ________ by chance．
