回复：那回国再回美国,在国内用签吗?

Technically, you need to get a new F-1 visa to come back if you go to China. But I suggest that you had better not go to China until you apply for green card (file I-485) and get AP just because your status is changed from B (B1/B2) status to another status (e.g. F1)and this will make you very difficult to get a new type of visa in China. Many people like you have terrible trouble in visa application in China.

So, please keep my suggestion deeply in your mind.