Peter didn't know was his.
whichever
which
whomever
who

Your answer should be “b”

Dogs have been considered man’s best friend for decades! most likely because of their kind and loyal nature. they make splendid companions. their loyalty is beyond compare and after all, a dog is the only thing on earth that loves you more than he loves himself! dogs see us as their friends and leaders, they’ll do anything in their power to ensure your comfort and safety.