为什么many fruit fruit要加s而some fruit不用加s

为什么many fruit fruit要加s而some fruit不用加s 为什么a lot of fruit fruit不加s而many fruits 加s buy some fruit fruit为什么不加s 为什么在用fruit的不用加s,而vegetable要加s呢? 为什么fruit不加s,而vegetable加s fruit什么时候加s? fruit什么时候加s 为什么Eat lots of fruit and vegetables中fruit不加s,而vegetable加s, many fruit fruit加不加s mangoes are my favourite fruit.fruit要加s吗 I want to buy many different kinds of fruit.fruit要加S吗? fruit在什么时候加s