The available options are:
A. an external force based on friendship
B. an external force based on setting
C. an internal force based on instinct
D. an internal force based on feelings
Answer:
B. an external force based on setting
Explanation:
From the excerpt, it can be concluded that White Fang understood the in and out of the wood setting compared to the other dogs. This is perfectly described as White Fang quickly moves between the running water and near-by thicket, while losing the trail of the chasing dogs. However it's an external force because this activity of White Fang running to the wood is caused by the chasing dogs.
