Final answer:
Surfactant prevents alveoli collapse and increases gas exchange in the lungs.
Step-by-step explanation:
The correct answer is C) decrease gas exchange.
Surfactant is a substance produced by type II alveolar cells in the lungs. Its main function is to reduce surface tension in the alveoli to prevent them from collapsing during expiration. By reducing surface tension, surfactant helps alveoli to expand and increases gas exchange.
Therefore, the correct answer is C) decrease gas exchange, as surfactant actually promotes gas exchange by maintaining the integrity of the alveoli and preventing collapse.