1. They often go swimming on Sundays. They have much free time then.
-> They often go swimming on Sundays when they have much free time.
2. She is not free, so she cannot join in our trip
-> If she was free, she could join in our trip.
3. "Thank you very much for helping me with these assignments," Tom said to me
-> Tom thanked me for helping him with those assignments.
4. How often does the mechanic service your car?
-> How often is your car serviced by the mechanic?