Given a scientific question, generate a correct answer to it.

Input: Consider Input: What process is involved in the formation of a waterfall, when a stream flows from an area of harder to softer rock?

Output: erosion

Input: Consider Input: Bacterial dna is contained in one circular chromosome, located where?

Output: cytoplasm

Input: Consider Input: What chemical substances are secreted by animals that communicate by odor or taste?
Output: pheromones