The sizes of two matrices A and B are given. Find the sizes of the product AB and the product BA, whenever these products exist... A is 4x1, and B is 1x4. Find the size of the product AB. Select the correct choice below and, if necessary, fill in the answer boxes to complete your choices A. The size of product AB is 4 x 4. B. The product AB does not exist. Find the size of the product BA. Select the correct choice below and, if necessary, fill in the answer boxes to complete your choice OA. The size of product BA is B. The product BA does not exist.