为什么somebody help 中的help 不加s而nobody knows中的know就加s呢

I do not think he knows Chinese history中的know为什么加s Eating vegetables helps us to keep helthy中的help为什么加s Let him help you with English.中的help要加s吗? Your help has been very valuable.help为什么不加s 英语语法问题 I suggest that everyong help in some way.help为什么不加-s, Most of the people know it?其中Knows为什么不加"s"? 为什么let's have tomato中的tomato不加s? today's newspaper中的newspaper 为什么不加s heavy rain中的rain为什么不能加s,而strong winds为什么可以加s? He must try to help his sister with her math?为什么try不加s when someone hieps you为什么在help后加S doing exercise helps,为什么help要加s