Triangle, circle, and square. So, assuming that is all that's in the pattern theenn:
Triangle: 1 Triangle: 4 Triangle: 7 Triangle: 10 Triangle: 13
Circle: 2 Circle: 5 Circle: 8 Circle: 11 Circle: 14
Square: 3 Square: 6 Square: 9 Square: 12 Square: 15
So your answer is the square c: Unless that's not what you needed to do. Not entirely sure on that.