Rewrite the following sentences without changing in meanings:
1. Don't stop him from doing what he wants.
-> Let him................
2. Tom has arranged to have dinner with Ann on Friday.
-> Tom is...........
3. We started learning English when we were in grade six.
-> We've...........
4.Someone has taken some of my books away.
-> Some of my books............
5. Tom doesn't smoke cigarettes any more.
-> Tom used.........