We want some fruit.和 He can eat fruits.为什么一个加S一个不加?

We want some fruit.和 He can eat fruits.为什么一个加S一个不加? Why don't we take some fruits?fruit不是不可数名词吗,为什么又加s? he can eat some foods 为什么can不加s不是第三人称单数加动词加s吗 为什么a lot of fruit fruit不加s而many fruits 加s we eat lots of vegetables and fruit 为什么fruit不加s a lot of fruit为什么不加s many fruits却加s buy some fruit fruit为什么不加s 为什么Eat lots of fruit and vegetables中fruit不加s,而vegetable加s, 请问:Eat some vegetables and fruit every day.为何fruit不加s? do moring exercises 和 do some exercise 为什么一个加s 一个不加 为什么many fruit fruit要加s而some fruit不用加s 为什么fruit可以不加s也可以加s?