what do you think is the most useful invention in the world

不行.因为" do you think " 是插入语,（插入语的意思是,你可以把它省略,句子仍通顺）下面我们来看,把do you think 去掉以后,如果换了,就是：what the most useful invention is in the world?明显这不符合英语语法规...怎么就不可以把the most useful invention is 理解成是think的从句呢？这个我们老师多次讲过，do you think在这里就 是个插入语，没有实际意义，所以这里它木有接从句的功能，也接不了从句。