1 如果你会合并下列句子,你的这个问题就OK了：
He came She was wating
1 When he came,she was waiting
2 While she was waiting,he came
3 She was waiting when he came
4 He came while she was waiting
2 主句为祈使句或含有情态动词时：
1 Give this book to Tom when he comes tomorrow (从句是一般现在时---连接词是when)
2 Tom.you must be quiet while Kate is doing her homework (从句是现在进行时----连接词是while)
3 Return the book to me when you have finished reading it (从句是现在完成时-----连接词是when)