Which of the following have thick walls?

Options

A. Artery
B. Vein
C. Both A & B
D. Capillaries

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which of the following blood vessels have thick walls. The options provided are arteries, veins, both A and B, and capillaries.

2. **Analyzing Each Option**:
- **Arteries**: Arteries have thick, muscular walls. This is because they carry blood away from the heart under high pressure. The thick walls help them withstand the pressure and maintain blood flow.
- **Veins**: Veins have thinner walls compared to arteries. They carry blood back to the heart at a lower pressure, so they do not need to be as thick.
- **Both A and B**: Since veins do not have thick walls, this option is incorrect.
- **Capillaries**: Capillaries are the smallest blood vessels and have walls that are only one cell thick. This allows for efficient exchange of gases and nutrients, but they do not have thick walls.

3. **Conclusion**: Based on the analysis, the only option with thick walls is **arteries**. Therefore, the correct answer is arteries.

### Final Answer:
**Arteries have thick walls.**

---