Decide whether the following statements are right or wrong.

a) If A + B is defined, then B + A is always defined.

b) The size of AB is always the same as the size of BA if AB is defined.

c) If A and B both have an inverse, then A + B has an inverse as well (in all cases).

d) If A,B and C are all square matrices of the same size, and if AB = D, then C D and D C are square matrices of the same size.