Given the task definition and input, reply with output. In this task, you are given two facts, and a multiple-choice question. Based on the given facts, answer the question with index of the correct option (e.g, "A").

Fact1: howling is used to warn other wolves by wolves, Fact2: Warnings and cautions are there for a good reason., Question: What kind of sound is used by wolves to caution other wolves? (A) whiplash (B) howling (C) a growling sound (D) several (E) a sniffing sound (F) noise (G) shaking (H) sound
B