4．_________________________(那是谁的包) is not known at that time.

5．It remains a mystery____________ __ (为什么这种动物突然灭绝了)．

Ⅱ.用适当的连接词完成下列句子

1．___________ he got the first prize in the English Contest surprised all of us.

2．__________ they would support us was a problem.

3．________ will take the place of Mr.Li as our new headmaster hasn't been decided.

4．___________ caused the accident to happen hasn't been made clear yet.