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?