()铸铁因为其性能硬脆,难以加工,主要用做炼钢原料。
A.麻口铸铁
B.白口铸铁
C.灰口铸铁
D.球墨铸铁
参考答案:B
—_____ do you go to the school library? —Once a week.
A.How often
B.How soon
C.How long
D.How much
《自然》杂志的影响因子为多少?()
A.31
B.32
C.33
D.34