Consider the statement, "For all integers a and b, if the product of a and b is even, then a is even or b is even." What would be the beginning of a proof by contrapositive of this statement?

Group of answer choices

Assume that either a or b are odd. We must show that ab is odd.

Assume that a and b are both odd. We must show that ab is even.

Assume that a and b are both even. We must show that ab is even.

Assume that a and b are both odd. We must show that ab is odd.