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 2 x 1, B is 1 x 1. O AB is 2 x 2, BA is 1 x 1. O AB is 2 x 1, BA is undefined. O AB is 1 x 2, BA is 1 x 1. O AB is undefined, BA is 1x 2