Read this excerpt from the call of the wild.

on the opposite slope of the watershed they came down into a level country where were great stretches of forest and many streams, and through these great stretches they ran steadily, hour after hour, the sun rising higher and the day growing warmer. buck was wildly glad. he knew he was at last answering the call, running by the side of his wood brother toward the place from where the call surely came. old memories were coming upon him fast, and he was stirring to them as of old he stirred to the realities of which they were the shadows. he had done this thing before, somewhere in that other and dimly remembered world, and he was doing it again, now, running free in the open, the unpacked earth underfoot, the wide sky overhead.

which theme is best supported by this passage?

a one's true nature will always prevail.
b buck is very similar to a wolf.
c nature is beautiful and powerful.
d animals are meant to run outside