**Core Concept**
Erythropoietin (EPO) is a hormone produced primarily in the kidneys that regulates red blood cell production in the bone marrow. Its production is stimulated by hypoxia, a condition characterized by insufficient oxygen delivery to tissues.

**Why the Correct Answer is Right**
In conditions of hypoxia, the kidneys sense the decrease in oxygen levels and respond by increasing the production of EPO. This leads to an increase in red blood cell production, which helps to compensate for the decreased oxygen delivery. The conditions that typically lead to increased EPO production include chronic obstructive pulmonary disease (COPD), high-altitude environments, and anemia of chronic disease. **Option A (Chronic obstructive pulmonary disease (COPD))** is a condition that leads to hypoxia, and therefore, EPO levels are typically increased.

**Why Each Wrong Option is Incorrect**
**Option B:** Polycythemia vera is a myeloproliferative disorder characterized by excessive production of red blood cells, which leads to increased EPO levels.
**Option C:** Renal cell carcinoma can produce EPO ectopically, leading to increased EPO levels.
**Option D:** (No option provided)

**Clinical Pearl / High-Yield Fact**
It's essential to remember that EPO levels can be elevated in conditions of tissue hypoxia, and this can be a useful diagnostic clue for clinicians.

**Correct Answer:** D.