单项选择题
A.10°~15° B.15°~25° C.25°~30° D.30°~40°
A.35钢 B.45钢 C.高速钢 D.轴承钢
A.16~20/25mm×25mm B.12~16/25mm×25mm C.20~25/25mm×25mm D.>25/25mm×25mm