--Why does the lake smell terrible? ---Because large quantities of water ______.
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A
have polluted
B
is being polluted
C
has been polluted
D
have been polluted
推荐题目
A library with seven thousand books _____ to the area as a gift.
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A
is offered
B
have offered
C
are offered
D
has offered
Many a student ________ failed in the biology exam，and Tom is the only one of them who ________ decided to give up the course.
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A
have；has
B
have；have
C
has；have
D
has；has
The Smiths ______ their breakfast when the doorbell rang.
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A
had
B
has been having
C
are having
D
were having