Read this excerpt from White Fang. Furthermore, it was remarkably easy to overthrow a dog taken by surprise; while a dog, thus overthrown, invariably exposed for a moment the soft underside of its neck—the vulnerable point at which to strike for its life. White Fang knew this point. It was a knowledge bequeathed to him directly from the hunting generation of wolves. So it was that White Fang's method, when he took the offensive, was: first, to find a young dog alone; second, to surprise it and knock it off its feet; and third, to drive in with his teeth at the soft throat.

Which best describes the force that influences White Fang’s fighting method?

an external force based on setting
an external force based on authority
an internal force based on feelings
an internal force based on instinct