Valves occur in

Options

A. Arteries, veins and auricles
B. Atria , ventricles and veins
C. Arteries , veins and ventricles
D. SA node, AV node and veins

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks where valves occur in the circulatory system. Valves are crucial components that help regulate blood flow and prevent backflow.

2. **Identifying Locations of Valves**: Valves are primarily found in two main areas:
- **Heart**: Valves are located between the chambers of the heart and at the exits of the heart into the major arteries.
- **Blood Vessels**: Valves are also present in veins, particularly in the limbs, to prevent the backflow of blood as it returns to the heart.

3. **Types of Valves in the Heart**:
- **Atrioventricular Valves**: These include the tricuspid valve (between the right atrium and right ventricle) and the bicuspid (or mitral) valve (between the left atrium and left ventricle).
- **Semilunar Valves**: These include the aortic valve (between the left ventricle and the aorta) and the pulmonary valve (between the right ventricle and the pulmonary artery).

4. **Valves in Veins**: Valves in veins are particularly important in the limbs to assist in the upward flow of blood against gravity, preventing backflow.

5. **Conclusion**: Based on the above points, valves occur in the following locations:
- **Atria** (specifically between atria and ventricles)
- **Ventricles** (specifically at the exits of the ventricles)
- **Veins** (to prevent backflow of blood)

### Final Answer:
Valves occur in the **atria, ventricles, and veins**.

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