Compute each matrix sum or product if it is defined. If an expression is undefined, explain why. Let A =, B =,C =, D =,and E = A + 3B, 4C - 2E, DB, EB Compute the matrix sum A + 3B. Select the correct choice below and, if necessary, fill in the answer box with in your choice. A + 3B = (Simplify your answer.) The expression A + 3B is undefined because B is not a square matrix. The expression A + 3B is undefined because A is not a square matrix. The expression A + 3B is undefined because A and 3B have different sizes. Compute the matrix sum 4C - 2E. Select the correct choice below and, if necessary, fill in the answer box within your choice. 4C - 2E = (Simplify your answer.) The expression 4C - 2E is undefined because the number of rows in C is not equal to the number of columns in E. The expression 4C - 2E is undefined because 4C and 2E have different sizes. The expression 4C - 2E is undefined because E is not a square matrix. Compute the matrix product DB. Select the correct choice below and, If necessary, fill in the answer box within your choice. DB = (Simplify your answer.) The expression DB is undefined because the number of rows in D is not equal to the number of columns in B.