A premature infant, when born, had low Apgar scores and was having difficulty breathing. The NICU physician injected a small amount of a lipid mixture into the child's lungs, which greatly reduced the respiratory distress the child was experiencing. In addition to proteins, a key component of the mixture was which one of the following?

The premature infant is experiencing respiratory distress syndrome, which is caused by a deficiency of lung surfactant. The lung cells do not begin to produce surfactant until near birth, and premature infants frequently are not producing sufficient surfactant to allow the lungs to expand and contract as needed. The surfactant is composed of a number of hydrophobic proteins and dipalmitoyl phosphatidylcholine. Sphingomyelin, gangliosides, triglyceride, and prostaglandins are not the components of the surfactant. The phosphatidylcholine content of the surfactant is 85% of the total lipids associated with the complex.