工序是港口装卸作业的基本生产环节。()
参考答案:对
–What ___ the number of the students in your school?
–About two thousand. A number of them_____ from England.
A.is; are
B.is; is
C.are; is
D.are; are
奥氏体化的钢冷却速度过快时,易出现()。
A、铁素体
B、马氏体
C、奥氏体