弯曲件回弹表现形式有（）方向。
A、一个
B、两个
C、三个
D、四个
参考答案：B
Alice has gone to the classroom and she didn't say _____. [ ]
A. when did she come back
B. when would she be back
C. when she came back
D. when she would be back
铜锌二元合金又叫（）。
A．普通黄铜
B．青铜
C．白铜
D．特殊黄铜
