Have to (in its correct form). sometimes it is possible to use either; sometimes only have to is possible. examples: well, it's 10 o'clock. i must (or have go now. ann was feeling ill last night. she had to leave the party early. 1 you work harder if you want to pass that examination. 2 many children in wear uniform when they go to school. 3 last night don suddenly became ill. call the doctor. 4 ann wear glasses since she was eight years old. 5 i'm afraid i can't come tomorrow. work late. 6 i'm sorry i couldn't come yesterday. work late. 7 tom go away next week. 8 we couldn't repair the car ourselves. take it to a garage. 9 when you come to london again, come and see us.

1 You really .have to.. work harder if you want to pass that examination.
2 Many children in Britain..have to... wear uniform when they go to school.
3 Last night Don suddenly became ill. We..had to... call the doctor.
4 Ann has...had to.. wear glasses since she was eight years old.
5 I'm afraid I can't come tomorrow. I..have to... work late.
6 I'm sorry I couldn't come yesterday. I..had to... work late.
7 Tom may..have to... go away next week.
8 We couldn't repair the car ourselves. We..had to.. take it to a garage.
9 When you come to London again, you  must come and see us.