signal analysis

例句：

1. 1. The police officer signaled to the driver to slow down.
   警察向司机示意减速。
2. 2. The car's horn is a signal for the driver to stop.
   汽车的喇叭是司机停车的信号。
3. 3.The fire department sent out a distress signal when they received the call.
   消防部门接到报警后发出了求救信号。