**Core Concept**
The lungs have several non-respiratory functions, including immune system modulation, hormone production, and the regulation of pH through ventilation.

**Why the Correct Answer is Right**
One of the most significant non-respiratory functions of the lungs is the production of surfactant, which is a complex mixture of phospholipids and proteins. Surfactant is secreted by type II pneumocytes and reduces surface tension within the alveoli, facilitating easier lung expansion during inspiration. This function is crucial for maintaining normal lung mechanics and preventing conditions such as atelectasis and acute respiratory distress syndrome (ARDS). Additionally, the lungs also play a role in the immune system, with resident macrophages and dendritic cells helping to filter out pathogens and other foreign substances from the inhaled air.

**Why Each Wrong Option is Incorrect**
* **Option A:** While the lungs do contain a significant amount of blood, their primary function is not to store blood. This option is incorrect because it does not accurately reflect a non-respiratory function of the lungs.
* **Option B:** Although the lungs are involved in the regulation of pH through ventilation, this is a respiratory function. This option is incorrect because it does not accurately reflect a non-respiratory function of the lungs.
* **Option C:** While the lungs do contain lymphoid tissue, their primary function is not to produce hormones. This option is incorrect because it does not accurately reflect a non-respiratory function of the lungs.

**Clinical Pearl / High-Yield Fact**
The lungs also play a role in the production of certain hormones, such as erythropoietin, which is involved in the regulation of red blood cell production.

**Correct Answer:** C.