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

Input: Consider Input: Passage: The heart is a muscular organ in the chest that consists mainly of cardiac muscle. It pumps blood through blood vessels by repeated, rhythmic contractions. Blood flows through four chambers of the heart when it beats. Heartbeat is controlled by electrical signals from special cells within the heart called the pacemaker. Answer: cardiac muscle

Output: What type of muscle makes up most of the heart?

Input: Consider Input: Passage: Mutations have many possible causes. Some mutations occur when a mistake is made during DNA replication or transcription. Other mutations occur because of environmental factors. Anything in the environment that causes a mutation is known as a mutagen . Examples of mutagens are shown in Figure below . They include ultraviolet rays in sunlight, chemicals in cigarette smoke, and certain viruses and bacteria. Answer: mutation

Output: What is it called when a mistake occurs in dna replication.

Input: Consider Input: Passage: When wood burns, it changes to ashes, carbon dioxide, water vapor, and other gases. You can see ashes in the wood fire pictured here. The gases are invisible. Answer: carbon dioxide
Output: What is the primary gas produced from burning of wood?