单项选择题
A.9.8 B.13.7 C.16.7 D.6.4
A.D≤60mm,△f≤0.5mm B.D≤60mm,△f≤1.0mm C.D≤60mm,△f≤1.2mm D.D≤60mm,△f≤1.4mm
A.旋转 B.伸缩 C.旋转伸缩 D.前进时旋转,后退时不旋转