Which of the following waves is used for radiotherapy?

Options

A. X-rays
B. Gamma rays
C. UV rays
D. None

Explanation

To solve the question "Which of the following waves is used for radiotherapy?" we will analyze the options provided: x-rays, gamma rays, ultraviolet rays, and none of the above.

### Step-by-Step Solution:

1. **Understanding Radiotherapy**:
- Radiotherapy is a medical treatment that uses high doses of radiation to kill or damage cancer cells. It is important to identify which type of wave is commonly used in this treatment.

2. **Analyzing the Options**:
- **X-rays**: These are a form of electromagnetic radiation that can penetrate the human body. They are commonly used in medical imaging and also in some forms of radiotherapy.
- **Gamma rays**: These are also a form of electromagnetic radiation, typically emitted from radioactive materials. They are used in certain types of cancer treatments, but they are not the primary choice for radiotherapy.
- **Ultraviolet rays**: These rays are not used for radiotherapy. They are primarily associated with skin treatments and can cause skin damage.
- **None of the above**: This option suggests that none of the listed waves are used for radiotherapy, which is incorrect.

3. **Conclusion**:
- Among the options provided, x-rays are the most commonly associated with radiotherapy, particularly in imaging and treatment planning. Therefore, the correct answer is **x-rays**.

### Final Answer:
The wave used for radiotherapy is **x-rays**.