The roof fell ____ he had time to rush out.
| A．until | B．before | C．when | D．Since |
It was in the school __________ he had studied ___________ he began the important experiment.
| A．that; where | B．in which; which |
| C．where; that | D．where; in which |
I felt somewhat sad and was about to leave _________ something happened which drew my attention.
| A．unless | B．until |
| C．when | D．while |
— May I stop here?
— No, you ___________.
| A．mustn’t | B．might not |
| C．needn’t | D．won’t |
Everything ____________ into consideration, they believed themselves more and returned to their positions.
| A．to take | B．taken |
| C．to be taken | D．taking |
— Did you finish your homework yet?
— Yeah. We turned them in, and now they ___________.
| A．are grading | B．are graded |
| C．are being graded | D．have graded |