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By the time he es back, I’m sure we all these rooms of the lab. Therefore, he doesn’t have to return.
A. have cleaned
B. will be cleaning
C. will have cleaned
D. have been cleaning
网友回答
A. have cleaned
B. will be cleaning
(答案→)C. will have cleaned
D. have been cleaning
解析：可联系答.案.网客服索取。