根据首字母及汉语提示，完成下列单词的拼写，使句意通顺。

1. Do you think this kind of water is s_____(安全) for drinking?

2. He is writing on the blackboard with a piece of c_____ (粉笔).

3. Our teachers are all very s_____ (严格) with us students.

4. Tom i_____ (邀请) all his best friends to his birthday party last Sunday.

5. We have to c_____ (携带) a lot of books in our school bags every day.