**Core Concept:** The question pertains to the life span of red blood cells (RBCs), which are responsible for transporting oxygen from the lungs to the body's tissues. RBCs are produced in the bone marrow and have a specific lifespan before they are removed from circulation and destroyed by the spleen.

**Why the Correct Answer is Right:** The correct answer is **D** - "120 days." Red blood cells have a specific life span, which is approximately 120 days (4 months). This is due to the continuous production and replacement of RBCs, coupled with the gradual destruction of old or damaged RBCs by the reticuloendothelial system, particularly in the spleen.

**Why Each Wrong Option is Incorrect:**

A. **14 days:** This is an inaccurate estimation of the RBC lifespan, which is much longer due to the continuous production and replacement process.
B. **60 days:** While RBCs are not completely destroyed at once, this option is too long and does not accurately represent the gradual process of RBC destruction.
C. **10 days:** Similar to option B, this estimate is too short and does not reflect the actual RBC lifespan.

**Clinical Pearl:** Understanding the life span of red blood cells is crucial for recognizing anemia. Anemia occurs when the body has insufficient RBCs or reduced hemoglobin levels, leading to reduced oxygen delivery to tissues. Clinical scenarios involving anemia may include assessing the need for blood transfusion, investigating causes of anemia (e.g., iron deficiency, hemolysis), and understanding the appropriate duration for transfused RBCs to be effective in the recipient's body.

**Correct Answer:** **D** - 120 days