单项选择题
A.0.1-0.4 B.0.02-0.1 C.0.5-0.8 D.0.4－0.5
A.后倾5-10° B.垂直0° C.前倾5-10° D.后倾15-20°
A.铜 B.高铬钢 C.低碳钢 D.中碳钢
A.10°-20° B.30°-40° C.70°-80° D.20°-30°
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