27. The boy was busy doing his homework, onlyonce in a while to look out of the window.A.

发布时间：2020-08-15 02:32:10


27. The boy was busy doing his homework, only    once in a while to look out of the window.
A. stopping
B. to stop
C. stopped
D. having stopped

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(答案→)A. stopping
B. to stop
C. stopped
D. having stopped
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