1. I happened to be (looking) out of the window when I saw his car (approaching) the gate.
2. It has (been) ages since I last (saw) Nick. He is said (to have been married) Darcy and they are believed (to have left) the country.
3. We are going by sea but I'd rather we (went) by air. I (have never/been) a good sailor.
4. Listen to the birds (singing). You know, I recently bought a parrot, but now I am (thinking) of buying a canary bird. I want it to (sing) for me in the morning.
5. Look at her! She (has had her hair/cut). She looks gorgeous!
6. We’d better (hurry up)… I’d hate to (arrive) late. / I’d rather we (would not arrive) late.
2) You mustn't tell the boss what happened, or he'll fire you.
3) I don't have to wear a tie; I do it because i like wearing ties.
4)You mustn't smoke in here; smoking is not allowed.
5) I mustn't be late. It's the most important meeting of the year.
6)You don't have to go now; you can stay a bit longer.
7) Visitors to the zoo mustn't feed the animals.
8) You don't have to drive so fast; we have a lot of time.
9) We don't have to cook more; there's enough food.
10) You mustn't put salt in her food; the doctor said she can't eat salt.