问题补充:
单选题Hehadto___beforetheyfinishedthecoursebecausetheywerenotwelldisciplined.A.drop inB.drop outC.drop offD.drop by
答案:
B解析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。
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