Which property would be useful in proving that the product of two rational numbers is ALWAYS rational?
A) a/b + c/d = ad + bc/bd
B) a + b/cd = a/cd + b/cd
C) a/b * c/d = ac/bd
D) a/b ÷ c/d = a/b * d/c
C. A rational number is a number that can be expressed as the ratio of two whole numbers. The product of the rational numbers a/b and c/d are also equal to a rational number ac/bd.
