薄料层操作时，成品率降低的原因是（）。
A、透气性好
B、表层反矿量率高
C、台车速度快
D、有效风量大
参考答案：B
— I posted the letter a week ago.
— Then they________the letter by now. It usually takes four days. [ ]
A. can have received
B. must have received
C. would have received
D. should have received
根据《素问·举痛论》原文，引起“气耗”的原因是（）
A.寒
B.炅
C.悲
D.劳
E.恐
