**Core Concept**
The question tests the understanding of radiation sensitivity of various tissues, which is crucial in radiation oncology. **Radiosensitivity** refers to the susceptibility of cells, tissues, or organs to damage caused by ionizing radiation. This concept is essential in predicting the effects of radiation therapy on different tissues.

**Why the Correct Answer is Right**
Since the correct answer is not provided, I will give a general explanation. The least radiosensitive tissues are typically those with low mitotic activity, such as **bone**, **cartilage**, and **muscle**. These tissues are less sensitive to radiation because they have a lower rate of cell division.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific option, it's challenging to provide a detailed explanation. However, if Option A were a rapidly dividing tissue like **bone marrow** or **epithelial tissue**, it would be incorrect because these tissues are highly radiosensitive.
**Option B:** Similarly, if Option B were a tissue with high mitotic activity, it would be an incorrect choice.
**Option C:** If Option C were a tissue with moderate to high radiosensitivity, such as **liver** or **kidney**, it would also be incorrect.
**Option D:** Without knowing the specific options, it's difficult to provide a detailed explanation for each.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **radiosensitivity** is directly related to the rate of cell division. Tissues with high mitotic activity, such as **bone marrow** and **gastrointestinal mucosa**, are more sensitive to radiation than tissues with low mitotic activity.

**Correct Answer:** D. Bone