He had to before they finished the course because they were not well disciplined
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He had to___ before they finished the course because they were not well disciplined.
A.drop in
B.drop out
C.drop off
D.drop by
试题答案
B
这里的短语意思各不相同，drop out 退学,drop in /drop by 顺便拜访，drop off 下降，减少。