In each case either show that the statement is true or give an example showing it is

Question:

In each case either show that the statement is true or give an example showing it is false.
(a) If A + B = 0, then B = 0.
(b) A and AT have the same main diagonal for every matrix A.
(c) If A and B are symmetric, then kA + mB is symmetric for any scalars k and m.