I won’t be able to watch the concert on TV tonight because I_____ my homework at that time.[ ]

Did you find the missing couple in the mountain yesterday?——No, but we _____ to get in touch with them ever since

Work gets done _______ when people do it together,and the rewards are higher too.

The thought ______ he might fail in the exam worried him a lot.

When he was a little boy，he ______ on the farm