The sizes of two matrices A and B are given. Find the sizes of the product AB and the product BA, if the products are defined. A is 3 x 1, B is 1 x3. Choose the correct answer below. O A. AB is undefined, BA is 1 x 1. O B. AB is 3x3, BA is undefined. O C. AB is 3x3, BA is 1x 1. O D. AB is 1 x 1, BA is 3 x3