Theorem: If r and s are rational numbers, then the product of r and s is a rational number. Which facts are assumed in a direct proof of the theorem? r = a/b, and s = c/d, where a, b, c, d are integers and 0 rs = a/b, where a and b are integers a=0. and d = 0. r = a/b, and s = c/d, where a, b, c, d are integers and a #0 and c #0 rs = a/b, where a and b are integers b ± 0.