within the bounds of possibility
Possible. You worked so hard this semester that I think an A is within the bounds of possibility.
leave open the possibility of (something or doing something)
To maintain or create the possibility of something (happening in the future); to not prevent something (from taking place at some point). We parted ways, but we left open the possibility of working together again sometime.
beyond the realm(s) of possibility
Impossible. With my low test grades, I think that getting an A in this class is beyond the realms of possibility.
within the realm(s) of possibility
Possible; capable of happening. You worked so hard this semester that I think an A is within the realm of possibility.