Which statement shows the function of air pressure in controlling expiration?
a.) a decrease in air pressure within the lungs allows air to flow in.
b.) an increase in air pressure within the lungs allows air to flow out.
c.) a decrease in air pressure within the lungs causes them to contract.
d.) an increase in air pressure within the lungs causes them to expand.

The best and most correct answer among the choices provided by your question is the third option or letter C "A decrease in air pressure within the lungs causes them to contract."

Exhalation (or expiration) is the flow of the respiratory current out of the organism. In humans it is the movement of air out of the bronchial tubes, through the airways, to the external environment during breathing.

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