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

[EX Q]: Passage: Glutathione is a low-molecular-weight compound found in living cells that is produced naturally by the liver. Healthcare providers give glutathione intravenously to prevent side effects of chemotherapy and to prevent kidney problems. Answer: liver
[EX A]: Glutathione is a low-molecular-weight compound found in living cells that is produced naturally by what?

[EX Q]: Passage: The mass number is the number of protons plus the number of neutrons in an atom. For example, most atoms of helium have 2 neutrons, so their mass number is 2 + 2 = 4. This mass number means that an atom of helium has a mass of about 4 amu. Answer: protons and neutrons
[EX A]: What makes up the mass number of an atom?

[EX Q]: Passage: The many steps in the process of aerobic cellular respiration can be divided into three stages. The first stage, glycolysis, produces ATP without oxygen. Because this part of the cellular respiration pathway is universal, biologists consider it the oldest segment. Note that glycogen and fats can also enter the glycolysis pathway. The second stage is the Krebs Cycle, and the third stage is the electron transport chain. It is during the third stage that chemiosmosis produces numerous ATP molecules. Answer: aerobic cellular respiration
[EX A]:
Glycolysis, the krebs cycle, and the electron transport chain are stages in what process?