大红细胞直径为()
A.<6μm
B.>9μm
C.>10μm
D.>15μm
E.>20μm
参考答案:C
—May we start the meeting now?
—No, we ______. We ______ to start until the manager comes.[ ]
A. mustn't; are allowed
B. don't have to; are supposed
C. needn't; aren't allowed
D. can't; aren't supposed
零磨损因素的概念