题目内容：

用所给词的适当形式填空（5分，每空1分）

1.Can you tell me the ___________(important) of knowledge(知识)?

2.It’s not easy to ______________(communication) with a stranger.

3.Tell you the ___________ (true), I’ve never seen him before.

4.I have two ___________ (old) sisters.

5.She often falls _________ (sleep) in class.