低温回火，将钢件温度加热到（）℃。
A．500～700
B．250～500
C．150～250
D．100～150
参考答案：C
计算负荷是什么，准确进行负荷计算的意义？
In the early 1960s, the famous Swiss psychologist Piaget established his theory of ______ development.
