1. We don't know when the manager returns
2. Date of the meeting will have to be changed again.
3. Can you manage to write these reports by yourself?
4. It is hours since Mary rang.
5. The fog prevented us from driving.
6.  I remember that I saw Dr.Nam watched television several times

1. We don't know when the manager returns
2. The date of the meeting will have to be changed again 
3. Can you manage to write these reports by yourself?
4. It's hours since Mary rang
5. The fog prevented us from driving 
6. I remember that I saw Dr.Nam watched television several times