Which of the following matrix are not in row echelon form? A. (1 0 0; 0 1 0; 0 0 1) (It means the first row is (1 0 0); the second row is (0 1 0); the third row is (0 0 1) .) B. (1 0 0 1; 0 1 0 0; 0 0 1 2) C. (0 1 0 2; 1 0 2 0; 0 0 1 3) D. (1 0 1; 0 1 1; 1 0 0)