Điền ''if '' hoặc ''unless '' vào chỗ trống
1. ....................you had rung , he would have come
2. ...................you rang,he wouldn't come
3. I should never have found the house.................the policeman hadn't helped me
4. He wouldn't learn mich .......................he works harder
5. I won't go to the door.................I hear the bell
6. .....................my watch hadn't been right , we shouldn't have been late
7. ........................the clock had been right ,we shouldn't have been late
8. I won't write to him..............he writes to me
9. .......................you don't ring the bell,the servant won't come
10. He'll come...........................you ring the bell