Which statement describes surfactant?

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Surfactant is a lipoprotein secreted by pneumocytes type II that lines the thin water film coating the alveolar surface. Its main job is to reduce surface tension in that film, which prevents alveolar collapse during expiration and makes it easier for the lungs to re-expand on the next breath. This lowering of surface tension increases lung compliance and stabilizes the alveoli, a critical factor especially in tiny alveoli. The other cell types have different roles: type I cells form the actual gas-exchange surface, goblet cells secrete mucus to moisten and trap particles in the airways, and alveolar macrophages destroy bacteria.