球罐安装前应对（）各部位进行检查和验收
A.球瓣
B.支柱
C.基础
D.附件
参考答案：C
常在制造轮胎的橡胶中加入的耐磨物质是（ ）
A．二氧化锰
B．铁粉
C．炭黑
D．涤纶
— Which is more useful, listening or speaking?
— I think _____ of them are useful. [ ]
A. none
B. both
C. all
