Which of the following is the main component of surfactant, secreted by alveolar epithelial cells?

The surface-active component of the lung extract is called pulmonary surfactant. It is a complex consisting of about 85% to 90% lipids and 10% to 15% proteins. The lipid poion is about 85% phospholipid,approximately 75% of which is phosphatidylcholine, mainly dipalmitoyl phosphatidylcholine. There are 4 specific surfactant proteins: SP-A, SP-B, SP-C, and SP-D. Surfactant is manufactured by specialized alveolar cells known as type II alveolar epithelial cells. Ref: Levitzky M.G. (2013). Chapter 2. Mechanics of Breathing. In M.G. Levitzky (Ed), Pulmonary Physiology, 8e.