**Core Concept**
The lungs have multiple non-respiratory functions, including immune system components, endocrine functions, and the synthesis of certain proteins and enzymes. The lungs are also a major site for the production of surfactant, a substance that reduces surface tension in the alveoli.

**Why the Correct Answer is Right**
The correct answer is related to the production of surfactant in the lungs. Surfactant is a complex mixture of phospholipids and proteins that is produced by type II pneumocytes in the alveoli. It reduces surface tension in the lungs, allowing them to expand and contract more easily and preventing the alveoli from collapsing. This is essential for maintaining normal lung function and preventing conditions such as respiratory distress syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not correct because while the lungs do have some role in the production of certain hormones, it is not a major endocrine function.

**Option B:** This option is not correct because the lungs do not have a significant role in the production of blood cells.

**Option C:** This option is not correct because the pancreas is responsible for the production of digestive enzymes, not the lungs.

**Clinical Pearl / High-Yield Fact**
The lungs are responsible for producing surfactant, which is essential for maintaining normal lung function and preventing conditions such as respiratory distress syndrome.

**Correct Answer: C. Production of surfactant.**