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

Input: Consider Input: Passage: Optical telescopes are designed to collect visible light. The two types of optical telescopes are reflecting telescopes and refracting telescopes. Answer: reflecting and refracting

Output: What are the two types of optical telescopes?

Input: Consider Input: 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

Output: What makes up the mass number of an atom?

Input: Consider Input: Passage: Gas solubility decreases as the temperature increases. Answer: decreases
Output: What happens to gas solubility as the temperature increases?