A.普通碳素鋼 B.優(yōu)質碳素鋼 C.高級優(yōu)質碳素鋼 D.低碳鋼
A.1/10~1/15 B.1/30~1/40 C.1/60~1/80 D.1/80~1/100
A.杠桿原理 B.牛頓第二定律 C.摩擦原理 D.能量守恒定律