9. Indicate True or False, and give a short explanation. (a) (2 points) Every nonzero matrix A has an inverse A-1, (b) (2 points) Every matrix has a unique row echelon form. (c) (2 points) If x ker(T) then T(x + y) = T(y). (d) (2 points) If A and B are in Rnxn, then det(A + B) = det(A) + det (B).