The presence of temporary gills in the embryos of snakes, birds and man indicates that

Options

A. These embryos need gills for breathing
B. Ancestors of these animals had gills at one stage of evolution
C. Lungs evolved from gills
D. Medium in which these embryos develop resembles `O_2` rich water

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the significance of temporary gills present in the embryos of snakes, birds, and humans.

2. **Identifying the Structures**: Recognize that these temporary gills are not functional gills but rather structures that appear during the embryonic development of these organisms.

3. **Linking to Evolution**: The presence of these gill structures suggests that the ancestors of these animals had gills. This is a reflection of evolutionary history, where certain traits are retained during development.

4. **Concept of Ontogeny and Phylogeny**: Understand the concept of "ontogeny recapitulates phylogeny," which means that the development of an organism (ontogeny) reflects the evolutionary history (phylogeny) of that organism. This means that as embryos develop, they exhibit features that were present in their ancestors.

5. **Examples of Development**: In the case of humans, during early embryonic stages, structures resembling gills and a tail are present. These features indicate that humans share a common ancestry with fish and reptiles.

6. **Conclusion**: Therefore, the presence of temporary gills in the embryos of snakes, birds, and humans indicates that their ancestors had gills at one stage of evolution.

7. **Final Answer**: The correct answer is that the presence of temporary gills in these embryos indicates that their ancestors had gills at one stage of evolution.

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