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

Example Input: What is defined as a repeating series of events that include growth, dna synthesis, and cell division?
Example Output: cell cycle

Example Input: The four major classes of biological macromolecules include carbohydrates, lipids, proteins, and what else?
Example Output: nucleic acids

Example Input: The most important characteristic of extant amphibians is a moist, permeable skin used for this?
Example Output:
cutaneous respiration