Answer this question by process of elimination.
Begin with A: if you plug in 1 for k, r = 13, so you can already rule out
A. Plug in a few more values for k (both odd and even), and you will
see that r is always odd. You could easily eliminate the others by
plugging in numbers. Plugging in 1 like before proves that C and
E are not necessarily true. Plug in 3, and you will find that D is
not necessarily true. So the answer must be B.