问题
选择题
Smoking is not allowed in the workplace because the air must be ____________. [ ]
A. keep clean
B. kept cleaning
C. kept clean
D. kept to clean
答案
答案：C
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Smoking is not allowed in the workplace because the air must be ____________. [ ]
A. keep clean
B. kept cleaning
C. kept clean
D. kept to clean
答案：C