A.1~2mm,2mm B.0~1mm,2mm C.1~2mm,3mm D.1~2mm,4mm
A.15km/h B.45km/h C.60km/h D.160km/h
A.鋼軌修理 B.預(yù)打磨 C.預(yù)防性打磨 D.修理性打磨