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

Input: Consider Input: Passage: Membranes Biological membranes surround cells and serve to keep the insides separated from the outsides. They are formed of phospholipid bilayer1 s, which by definition are a double layer of fatty acid2 molecules (mostly phospholipid3 s, lipids containing lots of phosphorus). Proteins4 serve very important functions in cellular membranes. They are active transports in and out of the cell, acting as gatekeepers. They relay signals in and out of the cell. Proteins are the site of many enzymatic reactions in the cell, and play a role in regulation of cellular processes. Answer: biological membranes

Output: What is it that surrounds cells and serve to keep the insides separated from the outsides?

Input: Consider Input: Passage: Humans learn behaviors through conditioning, as well. A young child might learn to put away his toys by being rewarded with a bedtime story. An older child might learn to study for tests in school by being rewarded with better grades. Can you think of behaviors you have learned by being rewarded for them?. Answer: conditioning

Output: How do humans learn behaviors?

Input: Consider Input: Passage: Vertebrate Endoskeletons. The vertebrate endoskeleton includes a vertebral column, cranium, limbs, and limb girdles. Can you find these parts in each endoskeleton shown here?. Answer: limb girdles
Output: The vertebrate endoskeleton includes a vertebral column, cranium, limbs, and what else?