未知题型 按O"Leary设计的菌斑记录法，控制良好的标准是菌斑至少为（）

单项选择题 采用电话闭塞法组织行车时，一个闭塞区段只允许一个列车占用，客车驾驶模式为（）

未知题型 气体在流道中经过突然缩小的断面（如管道上的针形阀、孔板等），产生强烈的涡流，使压力下降，这种现象称为节流。如果在节流过程中气体与外界没有热交换，就称为绝热节流。Gas in the flow channel through the sudden reduction of section (such as the needle valve on the pipe, orifice plate, etc.), the generation of strong eddy current, pressure drop, this phenomenon is called throttle. If there is no heat exchange between the gas and the outside world during throttling, it is called adiabatic throttling.