电主轴具有的优点包括( )
A. 简化结构,促进机床结构模块化
B. 降低机床成本,缩短机床研制周期
C. 改善机床性能,提高可靠性
D. 高档数控机床、如并联运动机床的特殊要求
He writes on both sides of the sheet to ________ paper.
A. converse
B. convert
C. conserve
D. consent
The computer laboratory is an essential ______ for students.
A. source
B. force
C. resource
D. reinforce