What you are given is that P true for an even number implies it true for the next even number. So if P(2n) where true for some n it is true for all subsequent n by induction.

So potentially both (b) and (c) are true as they clain proof of P(2n) which is all that can be said.

(b) says that if P(2) is true then P(2n) is true for all n, which satisfies our requirement and so is true.

(c) is also true since (P(1) and P(2)) implies P(2) and so we are back at (b)

CB