检查单级离心泵时,应检查离心泵泵轴是否弯曲变形,与()接触处是否过热,是否有磨内圆的痕迹。
A.叶轮
B.轴套
C.压盖
D.轴承
参考答案:D
—Is everything _____ we need to do _______?
—Yes. You needn't worry about it. [ ]
A. which; has done
B. which; doing
C. that; has done
D. that; done
双极型晶体管是由两个背靠背PN结组成的,工作过程中涉及( )两种载流子的运动,所以称为双极型。
A.电子
B.二端
C.空穴
D.正电荷