当冲压钢件和厚的硬铝工件时,落压下模一般采用(),上模采用锌合金。
A.铅
B.锌合金
C.铸钢
D.塑料
参考答案:C
It's reported that Nanjing South Railway Station _______ at the end of this month.[ ]
A.has been completed
B.is completed
C.was completed
D.will be completed
下列有关物质的性质或应用的说法不正确的是 [ ]
A.二氧化硅是生产光纤制品的基本原料
B.水玻璃可用于生产黏合剂和防火剂
C.盐析可提纯蛋白质并保持其生理活性
D.石油分馏可获得乙烯、丙烯和丁二烯