单项选择题

It may be necessary to stop ______ in the learning process and go back to the difficult points in the lessons.

A. at a distance
B. at intervals
C. at case
D. at length
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单项选择题
The lecture which lasted about three hours was so （）that the audience couldn’t help yawning.

A. tedious
B. bored
C. clumsy
D. tired
单项选择题
Being ignorant of the law is not accepted as an （）for breaking the law.

A. excuse
B. intention
C. option
D. approval
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