It's a relative pronoun which introduces a relative clause.
I might be wrong but I don't think it is.
Answer:
He was part of an antislavery political party
The answer is D) extended metaphor.
The author employs an extended metaphor in the passage, using a multi-sentence implied comparison between the car's owner and an animal, most likely a dog. The author describes him as growling when guarding his prized possession, like a dog with his bone. He further extends the metaphor by warning that he may bite if you get too close.
