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

Q: Passage: The cardiovascular system moves nutrients and other substances throughout the body. Answer: cardiovascular system

A: Which human body system system moves nutrients and other substances throughout the body?
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Q: Passage: Bacteria are responsible for many types of diseases in humans. Answer: diseases

A: Bacteria are responsible for many types of what in humans?
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Q: Passage: Blood vessels are long, tube-like organs that form a complex network throughout the body. They transport blood to all the body's cells. There are three types of blood vessels: arteries, veins, and capillaries. Transfer of substances between the blood and cells takes place across the thin walls of capillaries. Answer: capillaries

A:
Arteries and veins are two of the three types of blood vessels, what is the third?
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