零件在热处理后要有较高的强度和硬度，并且要求（）。
A．变形量最小
B．韧性好
C．刚性好
D．不变形
参考答案：A
—Has he finished his essay
—I don't know. He（）it this morning.
A.has written
B.was writing
C.wrote
D.had written
水解作用
