Assertion : All birds, except the ones like koel (cuckoo) build nests for retiring and taking rest during night time (day time for noctumal)
Reason : Koel lays its eggs in the nests of tailor bird.

Options

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

Answer

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that all birds, except for some like the koel (cuckoo), build nests for resting during the night (or day for nocturnal birds).
- This statement is generally true as most birds do build nests for resting and raising their young.

2. **Understanding the Reason**:
- The reason states that the koel lays its eggs in the nests of the tailor bird.
- This statement is incorrect. Koels are known to be brood parasites, primarily laying their eggs in the nests of crows, not tailor birds.

3. **Evaluating the Relationship**:
- The assertion is true, but the reason is false. The koel does not lay its eggs in the nests of tailor birds, which makes the reason statement incorrect.

4. **Conclusion**:
- Since the assertion is true and the reason is false, the correct answer is that only the assertion is true.

### Final Answer:
- The correct option is that only the assertion statement is true.