What does your mother do to keep fit, Tom? —She usually ______ after supper.

Hurry up, Mike. You must get to the airport an hour before the plane________.

He is playing cards _______ his friends. [ ]

Scientists are now working _ humanoids(类人生物) because they can help people alot. [ ]

I wonder_______ you’ll water this kind of tree. —Once a week. [ ]