Assertion : Bird's embryo shows tooth buds for some time.
Reason : Ontogeny repeats phylogeny.

Options

A. If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion, then mark (1)
B. If both Assertion and Reason are true ,but the Reason is not the correct explanation of the Assertion, then mark (2).
C. If Assertion is true, but Reason is false , then mark (3)
D. If both Assertion and Reason are false. , then mark (4)

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that "Bird's embryo shows tooth buds for some time." This means that during the developmental stages of a bird embryo, there are structures that resemble tooth buds, even though adult birds do not have teeth.

2. **Understanding the Reason**: The reason provided is "Ontogeny repeats phylogeny." This concept suggests that the development of an individual organism (ontogeny) reflects the evolutionary history of that organism's species (phylogeny). In simpler terms, the embryonic development stages can show features that were present in the evolutionary ancestors of that organism.

3. **Connecting Assertion and Reason**: The assertion about bird embryos showing tooth buds can be explained by the reason. Birds evolved from ancestors that had teeth, and during the embryonic development, remnants of these ancestral features can still be observed, even if they do not persist into adulthood.

4. **Historical Context**: It is important to note that birds lost their teeth around 60 to 80 million years ago. However, the embryonic development still reflects this ancestral trait, which is consistent with the idea that ontogeny repeats phylogeny.

5. **Conclusion**: Both the assertion and the reason are correct. The reason provided is indeed a correct explanation for the assertion, as it elucidates why bird embryos show tooth buds despite adult birds lacking teeth.

### Final Answer:
Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.