A model or an experiment in a science class can help students see things which would ______ remain hidden.
_____from what he said, he must be the thief who has stolen the car.
Can you make sure _______ the gold ring?
It’s no good ________about his grades.
If he ________tomorrow, I could talk to him about it.
Ann is said ________ research in Africa, and she will come back next month.