Normally, I'll answer this with a valid reason (no bullshits); eg. current company is a temporary job, exploring different challenges/working enviroment and such. It depends on you, yourself on why are you leaving your current company for a new one. Don't have to worry on what they are going to ask you next because all they want to do is to evaluate your characteristic from the point you've given.

As I said, you have to tell why are you leaving based on your own reason. Is it because of higher pay? Or the new company offering permanent job? Or they are offering the job that you studied in your uni days?

Well, I guess your answer could touch on permanent basis work as well as the utilising what you have studied. That's all I could think of.

At times, the new company will pay compensation to your current one if they want you badly (for some reasons). However, I can't answer you that question because I have never encounter one before. Probably other forummers over here might able to help you on that. 3 months is quite long, I would say because normally companies required one month notice from employees.