氟

例句：

1. 1. The fluorescent lights in the room are very bright.
   房间里的荧光灯非常亮。
2. 2. Fluorine is a very reactive element.
   氟是一种非常活跃的元素。
3. 3. The fluoride in water can help prevent tooth decay.
   水中的氟可以帮助预防蛀牙。