简支钢梁桥，轨道钢轨防爬的关键技术在于合理确定桥上轨道（）的大小及分布。
A、阻力
B、扣压力
C、伸缩量
D、膨胀系数
参考答案：B
If we had received your L/C,we ______ shipment．
A．will effect
B．have effect
C．would have effected
D．had effected
危险化学品共分几类？
