方向是指轨道钢轨工作边沿（）的平顺程度。
A、纵向
B、横向
C、纵断面
D、平面
参考答案：A
— In which part of the play was _____ your brother appeared?
— In the last ten minutes. [ ]
A. that where
B. this when
C. it that
D. it where
管道保温层由哪些部分组成？
