SIGMETsare（）
A. Warnings of the occurrence of the significant weather hazards at aerodromes.
B. Warnings of the occurrence of the significant weather hazards
C. An area forecasts for low level flights.
D. Warnings of specified en-route weather phenomena which may affect the safety of low-level aircraft
间隔铁又称铁砖，它是保持尖轨跟端（Q）尺寸和连接尖轨与导轨的设备
道岔（Q）与基本轨或可动心轨尖端与翼轨不靠贴时，应及时修理或更换
护轨平直部分轮缘槽标准宽度为（Q）mm，如侧向轨距为1441mm时，则侧向轮缘槽标准宽度为48mm
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