泵的安装高度大于允许吸入真空度时，会（）
A.提高功率
B.降低功率
C.产生气蚀
D.避免气蚀
参考答案：C
)You can give the document to _______is in the office.However, _______to require a written paper for it.
A．who;make sure
B．whom;making sure
C．whomever;be sure
D．whoever;be sure
下列不属于计算机病毒的特点是（）。
A、隐蔽性
B、传染性
C、危险性
D、潜伏性
