为了提高铲运机的工作效率，常采用的开行路线有（）
A.“一”字形
B.环形
C.“Z”形
D.“U”形
E.“8”字形
参考答案：B, E
We ______ last night, but we went to the concert instead.
A．must have studied
B．might study
C．should have studied
D．would study
简述加涅的学习结果分类？
