Every individual _________ in a continually changing world of experience of which he or she is the center.
| A．exists | B．will exist | C．is existing | D．has existed |
Don't scold him; even an experienced engineer _____ make such a mistake after all.
| A．can | B．must | C．should | D．dare |
A survey of the opinions of scientists _____ that three hours of outdoor exercise a week
_____ good for our health.
| A．show; are | B．shows; is | C．show; is | D．shows; are |
It was last year _____ I visited the museum _____ you had visited.
| A．that; that | B．when, where | C．that; where | D．when; that |
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_____ when to leave, I could only stay at home, _____ nothing.
| A．Knowing not; done | B．Not having known; doing |
| C．Having not known; done | D．Not knowing; doing |
While building a tunnel through the mountain, _____.
| A．an underground lake was discovered | B．workers discovered an underground lake |
| C．there was an underground lake discovered | D．a lake was discovered underground |