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

Passage: An experiment is a controlled scientific study of specific variables. A variable is a factor that can take on different values. For example, the speed of an object down a ramp might be one variable, and the steepness of the ramp might be another. Answer: variable
In a controlled scientific study, what do you call a factor that can take on different values?

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
What type of muscle makes up most of the heart?

Passage: Mitosis occurs in four phases, called prophase, metaphase, anaphase, and telophase. Answer: telophase
The four phases of mitosis are prophase, metaphase, anaphase and what?