Which Describes the Role of Surfactant in the Respiratory System

Which describes the role of surfactant in the respiratory system?

A) Surfactant helps increase surface tension within the alveoli, thus preventing each alveolus from collapsing as air moves in and out during respiration.
B) Surfactant helps reduce surface tension within the alveoli, thus preventing each alveolus from collapsing as air moves in and out during respiration.
C) Surfactant provides a layer of protective mucus that covers a large portion of the membrane that lines the respiratory tree, thereby purifying the air during inhalation.
D) Surfactant helps increase surface area, which increases the rate of gas exchange within the alveoli.