one question

when i left China with Chinese passport, usually the border inspection in Beijing Capital Airport asked me for the green card or U.S. visa
But after you became a US citizen, you don't have green card anymore. When you leave China, at China airport, if you show the border inspection the Chinese passport, they will ask "do you will any US visa"? How will you handle it?
If you show them the U.S. passport, they will look for the China visa and the stamp when you entered China.
So, i wonder how people can enter China with Chinese passport and leave China with US passport