Q: The main organs of the cardiovascular system are the blood vessels and what else?


Read this paragraph and choose the correct option from the provided answers:

The main organs of the cardiovascular system are the heart and blood vessels. Both organs contain valves. Valves also are found in plumbing systems. They can be turned on or off to control the flow of water.

 Choices:

- alveoli

- capillaries

- lung

- heart


A:
heart