用所给单词的适当形式完成句子。

1.  Because of his             (care), a traffic accident happened to him.

2.  He used to behave ______ (bad) in class.

3.  He is rich in ______ (imagine).

4.  This happened at the beginning of the     _ __ (thirty) century.

5.  I've made a             (decide) to study hard,