Oxygen-rich blood from the lungs comes to the thin-walled upper chamber of the heart on the left. The left upper chamber (A) then relaxes. It then contracts and the blood is allowed to enter the next chamber (B), as it expands. When the muscular left lower chamber of heart contracts the blood is pumped out to the body via aorta.
Deoxygenated blood reaches from the body to the upper chamber on the right side of heart (C) and it expands. As this part contracts, the corresponding lower chamber (D) dilates. This transfers the blood to right ventricle, which in turn pumps it to the lungs for oxygenated.
Which of these correctly represents the label A,B,C and D in the above passage?

Options

A. A- Left atrium, B- Left Ventricle, C- Right atrium, D-Right ventricle
B. A- Right ventricle, B- Left atrium, C- Left Ventricle, D-Right atrium
C. A- Right atrium, B- Right ventricle, C- Left atrium, D- Left ventricle
D. A- Left ventricle, B- Right atrium, C- Right ventricle, D- Left atrium

Explanation

To solve the question regarding the labels A, B, C, and D in the passage about the heart's function, we will follow these steps:

### Step-by-Step Solution:

1. **Identify Chamber A**:
- The passage states that oxygen-rich blood from the lungs enters the thin-walled upper chamber on the left side of the heart. This chamber is known as the **left atrium**.
- **Label A = Left Atrium**.

2. **Identify Chamber B**:
- After the left atrium relaxes and contracts, the blood flows into the next chamber. This chamber is the muscular lower chamber that pumps blood to the body. This is known as the **left ventricle**.
- **Label B = Left Ventricle**.

3. **Identify Chamber C**:
- The passage describes deoxygenated blood arriving at the upper chamber on the right side of the heart. This chamber is referred to as the **right atrium**.
- **Label C = Right Atrium**.

4. **Identify Chamber D**:
- The passage mentions that as the right atrium contracts, the corresponding lower chamber dilates and receives blood. This lower chamber is known as the **right ventricle**, which pumps the deoxygenated blood to the lungs.
- **Label D = Right Ventricle**.

### Final Labels:
- A = Left Atrium
- B = Left Ventricle
- C = Right Atrium
- D = Right Ventricle

### Conclusion:
The correct representation of the labels A, B, C, and D in the passage is:
- A is Left Atrium
- B is Left Ventricle
- C is Right Atrium
- D is Right Ventricle