Explain how alfred's argument contradicts his initial assumption proving that the sum cannot be rational. a) if c is rational, either b or a would have to be rational as well. b) if a is rational, either b or c would have to be rational as well. c) if b is irrational, the difference of two rational numbers could never be equal to it. d) if a + b is rational, then a and a could be either rational or irrational.