**Core Concept**
The question is testing the sensitivity of different tissues to ionizing radiation, a critical concept in radiation oncology and radiobiology. The underlying principle is that tissues with rapidly dividing cells are more susceptible to radiation-induced damage.

**Why the Correct Answer is Right**
The correct answer is bone marrow, which contains hematopoietic stem cells responsible for blood cell production. These stem cells are highly sensitive to radiation due to their rapid cell division rate. When exposed to radiation, bone marrow cells undergo apoptosis, leading to a decrease in blood cell production. This can result in bone marrow failure, characterized by anemia, neutropenia, and thrombocytopenia.

**Why Each Wrong Option is Incorrect**
* **Option A:** Intestinal mucosa is sensitive to radiation, but it is not the most sensitive tissue. The intestinal mucosa has a high rate of cell turnover, but it can regenerate relatively quickly compared to bone marrow.
* **Option B:** The central nervous system (CNS) is relatively resistant to radiation, as it has a low rate of cell division. However, the CNS can still suffer damage from high doses of radiation, leading to neurotoxicity.
* **Option C:** The reproductive organs, such as the ovaries and testes, are sensitive to radiation, particularly at high doses. However, they are not as sensitive as bone marrow, which is more susceptible to radiation-induced damage.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the LD50 (lethal dose for 50% of the population) for radiation exposure is approximately 4-5 Gy for bone marrow, highlighting its extreme sensitivity to radiation.

**Correct Answer: C. Bone marrow**