shild sb.\sth. from sb.\sth.
在偏序集中，如果x，y∈A，有x≤y，且x≠y且没有其他元素Z，满足x≤z，z≤y，则称元素y盖住元素x，记作CovA={∣x，y∈A，且y盖住x}。
A. 对
B. 错
Under no circumstances will there be wage control while I am ______ of the government.
A. the head
B. a head
C. head
D. that head
When you go to the shops, please bring me ____.
A. a fruit can
B. a fruit's can
C. a can of fruit
D. many times
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