............... rays are used to stimulate the production of vitamin D in the body.

Options

A. UV
B. Cosmic
C. Dark
D. IR

Explanation

To solve the question regarding which rays are used to stimulate the production of vitamin D in the body, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks which type of rays are responsible for stimulating the production of vitamin D in the human body.

2. **Identify the Options**: The options given are:
- A) Ultraviolet
- B) Cosmic
- C) Dark
- D) Infrared

3. **Recall the Function of Each Type of Ray**:
- **Ultraviolet Rays**: These are a type of electromagnetic radiation that comes from the sun. They are known to play a significant role in the synthesis of vitamin D in the skin when exposed to sunlight.
- **Cosmic Rays**: These are high-energy radiation that comes from outer space. They do not have a known role in vitamin D production.
- **Dark Rays**: This term is not scientifically recognized in the context of electromagnetic radiation.
- **Infrared Rays**: These rays are primarily associated with heat and do not contribute to vitamin D synthesis.

4. **Determine the Correct Answer**: Based on the information about the roles of these rays, it is clear that ultraviolet rays are the ones that stimulate the production of vitamin D in the body.

5. **Fill in the Blank**: Therefore, the correct answer to the question is "ultraviolet".

### Final Answer:
Ultraviolet rays are used to stimulate the production of vitamin D in the body.

---