春秋时期，我国开始出现了 ____农具，这种农具和 ___技术的推广，使土地利用率和农作物产量提高。
铁；牛耕
—Do you often help your cousin with his English?
—No. He learns English by __________. [ ]
A. himself
B. yourself
C. herself
D. myself
高碳马氏体中碳化物析出方式是（）
A.M析出→εFeXC.→θFe3C
B.M析出→εFeXC.→Fe5
C.2→θFe3C.
