测量1Ω以下的小电阻,如果要求精度高,可选用( )。
A.单臂电桥
B.万用表×1Ω挡
C.毫伏表
D.双臂电桥
参考答案:D
In the past twenty years great changes _______in China.
A.were taken place
B.have been taken place
C.have taken place
D.were happened
安全生产许可证的有效期为几年?