移频机车信号中，当机车信号由显示红黄灯转为显示红灯时，表示机车已冒进显示红灯的（）。
参考答案：地面信号机
The old man ______live with his wife, but now he ______alone after she died. [ ]
A. used to; is used to live
B. used to; is used to living
C. was used to; used to live
D. is used to; is used to live
填料压盖的作用（）。
A、压紧填料
B、压紧密封环
C、密封高压室
D、压紧填料，密封低压室不至于大量漏水或漏气
