单项选择题
A.±1%B.±2%C.±3%D.±4%
A.180~240sB.120~180sC.60~120sD.30~50s
A.1mB.1.2mC.1.5mD.2m
A.10~20cmB.20~30cmC.30~50cmD.50~100cm
微信扫一扫,加关注免费搜题