Doubts about X2 Visa

Hi, next semester I will study in China, so I'm going to apply for a X2, is it possible to get a multiple-entry??? but I've already read that they are just for expended for 3 months, so if i must apply to anotther one in china, what will happen with my multiple-entries in case I still don't used?
Another question: If I want to apply, do i need to buy my plane tickets? I consulted that in some travel agencies, but i really think that they are just trying to send me the air tickets.
Thanks!