什么时候用 what are 什么时候用 what is

is后面加名词单数形式，are后面加名词复数形式或不可数名词。people呢，是这样的：there are many people,因为people是复数，而且肯定是很多个，所以要用many修饰。undersand?

what are you doing?

what are these? 一般询问可数的东东
what is it? 一般询问不可数的东东

what is the population of China?
中国有多少人口。

要看后面加什么就好了啊

复数(东西多)的时候用what are
例子: What are the books on the desk?

单数(一个东西)的时候用what is
例子: What is the book on the desk?

what are + 复数
what is + 单数

what are + 复数
what is + 单数 \不可数名词

询问具体数量的用 what are
一个总略（比如 population），单数的，不可数的用 what is