Then the rain came and the red flag went up to signal a halt.

当时，雨下了起来，红旗被升起，发出停止的信号。

《柯林斯英汉双解大词典》

At 9:30 am, the full red/yellow/green signal cycle might be 140 seconds.

上午九点半的时候，完整的红黄绿信号灯变换周期大概为140秒。

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Using the natural reflectivity of ceilings and walls, a transmitted infra-red signal can be received by any number of receivers within a room.

利用天花板和墙面的自然反射性，传送的红外信号能够被一个屋子里的所有接收器接收到。

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"I don't think we'll ever completely clear our rivers of red signal crayfish, " she said.

BBC: Study may help endangered white clawed crayfish

The native species is under threat from red signal crayfish, which were introduced to the UK in the 1970s and now dominate rivers.

BBC: Study may help endangered white clawed crayfish

The crash happened when a Thames Trains train driven by Michael Hodder, 31, went through a red signal and hit a London-bound Great Western express.

BBC: Paddington rail crash