轧件轧制面的尺寸调整主要是依靠调整（）来实现的。
A.R因子
B.辊缝
C.速度
D.轧制压力
参考答案：B
The train was late and many people were kept _________ at the railway station.
to wait B. to be waiting C. waiting D. waited
下列不属于PC机连网设备的是( )。
A．MODEM
B．摄像头
C．集线器
D．以太网卡
