The word "caterpillar" is originally a noun used to refer to a type of worm-like insect. Caterpillars are small and their bodies do not allow them to move rapidly. With that in mind, we can infer that an author who uses "caterpillar" as a verb wishes to convey the idea that something is moving slowing, crawling, just like a caterpillar. In conclusion, we can choose letter A as the best option.
