根据首字母及汉语提示，完成下列单词的拼写，使句意通顺。
Do you think this kind of water is s_____(安全) for drinking?
He is writing on the blackboard with a piece of c_____ (粉笔).
Our teachers are all very s_____ (严格) with us students.
Tom i_____ (邀请) all his best friends to his birthday party last Sunday.
We have to d_____ (携带) a lot of books in our school bags every day.