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

Example Input: Passage: Cloud types include cirrus, stratus, and cumulus. Answer: clouds
Example Output: Cirrus, stratus, and cumulus are types of what?

Example Input: Passage: The lungs of mammals are unique in having alveoli. These are tiny, sac-like structures. Each alveolus is surrounded by a network of very small blood vessels (see Figure below ). Because there are millions of alveoli in each lung, they greatly increase the surface area for gas exchange between the lungs and bloodstream. Human lungs, for example, contain about 300 million alveoli. They give the lungs a total surface area for gas exchange of up to 90 square meters (968 square feet). That's about as much surface area as one side of a volleyball court!. Answer: alveoli
Example Output: What in mammalian lungs, increases the surface area for gas exchange?

Example Input: Passage: Old age begins in the mid-60s and lasts until the end of life. Most people over 65 have retired from work, freeing up their time for hobbies, grandchildren, and other interests. Stamina, strength, reflex time, and the senses all decline during old age, and the number of brain cells decreases as well. The immune system becomes less efficient, increasing the risk of serious illnesses such as cancer and pneumonia. Diseases such as Alzheimer's disease that cause loss of mental function also become more common. Answer: old age
Example Output:
When does diseases like alzheimer's become more common?