Who invented the steam engine?

All of the educated students from china would answer it with out thinking,''It was James Watt."
That is our answer too in the International Trade class when Mr Yu asked us.
'I am sorry .You are wrong.' said Mr Yu,' He just improved it.'
But we had learn it in our elementary school from a text that it is James watt.
"That is wrong." said Mr Yu,"There are two mistakes in that article in my opinion. One is Watt just improved it.The other ,which I think is much more important is that the article indicate that invention is an easy job. Watt invent stream engine just beacaus he watched the water bubbled up in a pot."
-------------To be continuted