You can eliminate the 4th possible answer because it doesn't defy and specify your question. 1+1=0 will be taught in higher math standards. You can cross out the 1st possible answer because A and B are not given as 0. Your possible answers are the 2nd and the 3rd possible solutions. However, you have an clue on your question. The clue, "Not A", might mean the unknown variable is 0. My guess would probably be the 3rd possible answer.