Student X requires retour ticket?

My question is: Do I need to buy a return ticket for my application? I do know that it is necessary to book a flight beforehand when you apply for the visa, but I cannot find the information which says that I am required to buy a return ticket. I have not given much details from my university so I am not quite sure when to leave China which gives me some difficulties in finding a return ticket. It would be better for me if I can book only a flight to China and when I know the exact details about the duration of my stay (the only thing I know is that it is one academic year), I will buy a ticket back. But is this possible when applying for a visa? Also, can I ask for a double entry one if I apply for X1?