Are professors generally straight forward about admission decisions? I had applied for a PhD to some colleges in the US, and am waiting for admission results. A professor at a college that I am hoping I am accepted at has responded to my queries of "Is my application likely to be accepted, or should I just accept school B's offer?" with the same answer "your application will be considered in the second round, so you should wait for it. However, I cannot make any promises". 

I feel that if the professor thought I had a good chance of getting in, he might have stated so in his replies. "I can't make any promises" seems to be a polite but safe reply, indicating I might be accepted, but thechances do not appear too bright. Should I just accept school B's offer?
I take "I cannot make any promises" to mean ... I cannot [i.e., I won't] make any promises.  Behind that door could be anything.

In other words, it added no information to your decision about whether to respond in advance to School B's offer.

I wouldn't recommend asking the same professor again, but a more informative question for you to have asked would be when (with specific reference to the April 15th deadline that most graduate programs operate under) you would hear back.

Your best bet is to wait.