red flag
noun [ C ] uk/ˌred ˈflæɡ/ us/ˌred ˈflæɡ/
（用作危险信号的）示警红旗
a flag used as a sign of danger
You're not allowed to swim when the red flag is flying. 示警红旗升起的时候不允许游泳。
（象征革命的）红旗
a flag used as a symbol of revolution
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