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.
