单项选择题

By the year 2010, scientists probably ______ a cure for cancer.

A. will be discovering
B. are discovering
C. will have discovered
D. have discovered
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单项选择题
All flights ______ because of the snowstorm, we decided to take the train.
A. were canceled
B. had been canceled
C. having canceled
D. having been canceled
单项选择题
The policemen went into action______when they heard the alarm.
A. promptly
B. presently
C. quickly
D. directly
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