混凝土是（）材料。
A.完全弹性体
B.完全塑性体
C.弹塑性体
D.不好确定
参考答案：C
They ________ many difficulties during World War II, but they never lost confidence about life.
A．went over
B．went through
C．went up
D．went on
Ames试验最常用的实验方法是（）
A.共培养法
B.预培养法
C.平板掺入法
D.点试法
E.突变法
