I hadn't been reading for half an hour _____ I heard steps outside.
A. once
B. as soon as
C. while
D. when
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_____ you seem to know them, why don't you introduce me to them?
A. Since
Because
C. When
D. For
We'll let you use the room _____ you keep it clean and tidy.
A. when
B. where
C. while
D. on condition that
____ a jewel falls into the mud, it remains as precious as before.
A. While
B. If
C. For
D. Whether
The school _____ I visited last year was not the one _____ I once worked.
A. which; where
B. which; which
C. where; which
D. where; where