Question

1. what is the main function of the respiratory system?

to bring oxygen into the body and remove carbon dioxide
to pump blood throughout the body
to break down food into nutrients
to send messages through the nerves

Explanation:

• The respiratory system's primary role is gas exchange: inhaling oxygen ($O_2$) and exhaling carbon dioxide ($CO_2$).
• "To pump blood" is the circulatory system (heart/blood vessels).
• "To break down food" is the digestive system.
• "To send nerve messages" is the nervous system.

Thus, the first option matches the respiratory system’s function.

Answer:

A. To bring oxygen into the body and remove carbon dioxide