____ is a good form of exercise for both young and old.
The students were ____ over the ____ problem, listening to the teacher with a ____ expression on their faces.
The reason for his success is ______ he has worked very hard.
The weather turned out to be fine yesterday. I_____ the trouble to carry my umbrella with me.
I was about to leave the office ______ an unexpected visitor came. A. while B. as C when D. before
It was a matter of ________ would take the position.