Studies show that people are more __________ to suffer from back problems if they always sit before computer screens for long hours.
You _____ such a serious mistake if you had followed his advice.
If only I _____ my watch!
What should we do if it _____ tomorrow?
--- “What will you do during the summer holiday?” --- “I don’t know, but it’s high time _____ something.”
I’m glad I went over all my notes; otherwise _____ .