电机转子不平衡,会使电机运行时发生振动和噪声,加速()磨损,缩短电机的使用寿命。
A.轴承
B.风扇
C.转子铁心
D.密封圈
参考答案:A
房间隔缺损若在胸骨左下第4~5肋间隙处闻及短促与低频的舒张早中期杂音,该杂音产生的原理是()
A.主动脉瓣相对狭窄
B.肺动脉瓣相对狭窄
C.二尖瓣相对狭窄
D.三尖瓣相对狭窄
E.主动脉瓣相对关闭不全
Most of the boys in our class ________ playing football; only a ________ likes playing basketball. [ ]
A. like; majority
B. likes; majority
C. like; minority
D. likes; minority