what are they doing和what they are doing的区别

这两个句子的区别是：句型不一样，用法就不一样。

What are they doing?是由特殊疑问词What+一般疑问句构成，所以是个特殊疑问句，意思是“他们在干什么？”回答为：They are doing…他们在(做……)

What they are doing是由what+陈述句构成，因此是what引导的主语从句或宾语从句，如：

What they are doing is good for the country and people.他们做着的事利国利民。(what引导的主语从句)

I wonder what they are doing.

我想知道他们在做什么(what引导的宾语从句)。