用括号内所给词的适当形式填空
1. As a student, we must know the________(important) of study.
2. I hear you' ve s________(success) in giving a concert. Congratulations!
3. He usually stays up late at night and is often________(sleep) in class.
4. The teacher left the classroom without________(say)a word.
5. She didn't work hard at her lessons so she failed ________(pass) the exam.
6. Tom ________(not tell) to take part in the meeting last week.