[A] : In amphibians heart is two chambered.
[R]: The oxygenated blood is returned to the heart through sinus venosus.

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To analyze the assertion and reason statements provided in the question, we will break down the information step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "In amphibians, the heart is two-chambered."
- This statement is incorrect. Amphibians have a heart that is typically described as three-chambered (two atria and one ventricle) rather than two-chambered.

2. **Understanding the Reason (R)**:
- The reason states that "The oxygenated blood is returned to the heart through sinus venosus."
- This statement is also incorrect. In amphibians, the deoxygenated blood returns to the heart through the sinus venosus, while the oxygenated blood is returned through the pulmonary veins to the left atrium.

3. **Conclusion**:
- Since both the assertion (A) and the reason (R) are false, the correct answer to the question is that both A and R are false.

### Final Answer:
Both A and R are false.

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