机房由（）组成. ["曳引机","缓冲器","控制柜","平层装置"]
电梯曳引机主要由（）、联轴器、曳引轮、盘车手轮和底座等组成. ["电动机","电磁制动器","减速箱","缓冲器"]
电梯常用的蜗轮蜗杆减速箱有（）特点，所以得到广泛的应用 ["减速比大","传动平稳","噪声小","效率高"]
电梯发生事故而须作短程升降盘车的步骤有() ["断开轿厢电源","二人配合操作","断开轿顶电源","注意平层标志","渐进式松闸"]
交流双速电梯起动过程中在定子电路中串入电抗器是为了() ["改善运行效率","限制起动电流","改善舒适感","减少起动时间","加大起动电流"]
属于既往史的是()属于个人史的是()
