输油臂的一般组成部分有内、外臂、立柱、三向回转接头、内、外臂配重。
参考答案：对
允许速度大于120km/h的线路，轨距的变化率不得大于（）（不含规定的递减率）。
A.1‰
B.1.5‰
C.2‰
D.2.5‰
John ______ in his room when he heard screaming.
A．is studying
B．studied
C．was studying
D．has studied
