以下哪项驱动制动带接合?()
A.蓄压阀
B.真空调制阀
C.调速阀
D.伺服活塞
E.延时阀
参考答案:D
The boy is unfriendly, so he has ___________ friends. [ ]
A. few
B. a few
C. little
D. a little
下列物质中既含离子键,又含共价键的是 ( )
A.NaCl
B.MgCl2
C.H2O2
D.NaOH