Answer :
A. "howls" is correct. These can be confusing, because if it were just "wolves" it would be "howl", but since it's a "pack", which is singular, it's "howls". Try saying it out loud.
Answer:
A. howls
Explanation:
The verb "howl" in this sentence has to be in agreement with the word "pack" and not with the word "wolves", because the phrase says that one (1) pack of wolves howled, in this case "one pack" this in the singular, then the verb has to be in the singular also, in this case, the right alternative is "howls".