Fill in the blank with the right verb form. (用所给动词的正确形式填空。)

1. If he_________ (have) enough time tomorrow, he_________ (meet) you at his office.

2. When Ann called me, the barber_________ (cut) my hair.

3. If you _________ (help) others in trouble, you_________ (be) happy.

4. While he_________ (watch) a video at home, his best friend_________ (come) to see him yesterday

    afternoon.

5. What_________ (happen) if there is no water or air on the earth?