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

Example Input: Passage: Adolescents may have mood swings because of surging hormones. Answer: surging hormones
Example Output: Many adolescents experience frequent mood swings. name one of the causes for this.

Example Input: Passage: Muscles cannot contract on their own. They need a stimulus from a nerve cell to "tell" them to contract. Let's say you decide to raise your hand in class. Your brain sends electrical messages to nerve cells, called motor neurons, in your arm and shoulder. The motor neurons, in turn, stimulate muscle fibers in your arm and shoulder to contract, causing your arm to rise. Involuntary contractions of cardiac and smooth muscles are also controlled by nerves. Answer: stimulus
Example Output: What do muscles need to contract?

Example Input: Passage: Acids change the color of certain acid-base indicators. Two common indicators are litmus and phenolphthalein. Blue litmus turns red in the presence of an acid, while phenolphthalein turns colorless. Answer: acid
Example Output:
What causes blue litmus to turn red?