棱镜的偏向角
参考答案：
入射光线与出射光线的夹角（入射光线绕向出射光线顺正逆负）
Tom _____ full marks, but he was too careless and made a spelling mistake.
A．could gain
B．could have gained
C．must have gained
D．must gain
简述家长制管理方式的特征
