为什么不能用Where is he going to?

问题描述:

为什么不能用Where is he going to?
而只能用Where is he going?

where is he going to是一句还没有写完的将来时的句子,翻译过来就就是他打算去哪里做什么=where is he going to do sth.
而where is he going就是一个完整的句子‘他正要去哪儿?’