China Business F visa. Is it compulsory need the return flight book tickets?

because If i want to stay in china with F visa for 3 months, or more than. because may be chance i get extantion visa on there. so no possible to book for me return filght ticket 3 or more than months, so i want to know its compalsary to book flight tickets . And Also If its necessary to book flight tickets , so then il book tickets in china any airport from my destination to till any where for me cheap is that ok? or its need only final destination where or which city i want to go ? please reply me , Thank you.