Which among the following groups of organisms shows the closest relationship?

Options

A. Protochordates and fish
B. Annelids and nematodes
C. Amphibians and fish
D. Whales and fish

Explanation

**Step-by-Step Solution:**

1. **Understanding the Groups**: We need to analyze the groups of organisms provided in the options:
- Protocordates and fish
- Annelids and nematodes
- Amphibians and fish
- Whales and fish

2. **Analyzing Each Group**:
- **Protocordates and Fish**: Protocordates are primitive chordates that share some characteristics with fish, but they are not as closely related as other groups.
- **Annelids and Nematodes**: Both are types of worms, but they belong to different phyla and have significant differences in their anatomy and life processes.
- **Amphibians and Fish**: Amphibians (like frogs) and fish share a closer evolutionary relationship. Both groups have gills and fins at some stage of their life cycle. Amphibians typically have aquatic larval stages that resemble fish.
- **Whales and Fish**: Whales are mammals and while they live in water and have streamlined bodies similar to fish, they are not closely related in terms of evolutionary lineage.

3. **Identifying the Closest Relationship**:
- The amphibians and fish share more common traits, especially during their life cycles (gills and fins), and they also have similar reproductive methods (aquatic fertilization).
- Therefore, among the given options, amphibians and fish show the closest relationship.

4. **Conclusion**: The group that shows the closest relationship is **amphibians and fish**.