主要运输巷道铺设时在曲线段为防止因列车横向推力作用而使得轨距扩大，应设置什么设施？
参考答案：
轨距拉杆。
Jason has been preparing carefully for his English examination so that he could be sure of passing it at his first_________ .
A．purpose
B．desire
C．attempt
D．intention
亚音速流动，是指马赫数（）时的流动。
A.等于1
B.等于临界马赫数
C.大于1
D.小于1
