Given a scientific passage and an answer, generate a question for the given answer.

[EX Q]: Passage: Today, scientists think that electrons truly are fundamental particles that cannot be broken down into smaller, simpler particles. They are a type of fundamental particles called leptons. Protons and neutrons, on the other hand, are no longer thought to be fundamental particles. Instead, they are now thought to consist of smaller, simpler particles of matter called quarks. Scientists theorize that leptons and quarks are held together by yet another type of fundamental particles called bosons. All three types of fundamental particlesleptons, quarks, and bosonsare described below. The following Figure below shows the variety of particles of each type. Answer: quarks
[EX A]: What can protons and neutrons be broken down into?

[EX Q]: Passage: Types of neurons include sensory neurons, motor neurons, and interneurons. Answer: interneurons
[EX A]: Types of neurons include sensory neurons, motor neurons, and?

[EX Q]: Passage: Mammals generate heat mainly by keeping their metabolic rate high. The cells of mammals have many more mitochondria than the cells of other animals. The extra mitochondria generate enough energy to keep the rate of metabolism high. Mammals can also generate little bursts of heat by shivering. Shivering occurs when many muscles contract a little bit all at once. Each muscle that contracts produces a small amount of heat. Answer: metabolism
[EX A]:
Mammals generate heat primarily by maintaining a high rate of what?