照明灯管为什么是3根线

说的详细些，是不是通过开关可以改变亮度的。

There are four kinds of things on the platform,a bicycle key,a pair of sunglasses,a hair band,newspaper,whose are these things?We only know that in this class,Alice liks reading newspaper,Jack often rides a bike to school,Kathy hates sunshine,she likes to be cool,Lillian has long hair,Maris hates reading.So with these tips we can conclude that:the newspaper is Alice's,not Maris,the bike is Jacke's since only he ride a bike to school.The sunglasses is Kathy's cause the sunglasses can help her to prevent her eye from being basked by the sunshine,also wearing a pair of sunglasses will be cool in appearance.The hair band is Lillian's cause Lillian can use the hair band to prick her long hair.

一火一零一接地

火线、零线、地线