Crocodile and penguin are similar to whale and dog fish in which one of the following features?

Options

A. Possess a solid single stranded central nervous system
B. Lay eggs and guard them till they hatch
C. Possess bony skeleton.
D. Have gill slits at some stage.

Answer

To solve the question regarding the similarities between crocodiles, penguins, whales, and dogfish, we will analyze the provided options step by step.

### Step-by-Step Solution:

1. **Identify the Animals**:
- Crocodile and penguin are both reptiles and birds, respectively, while whale is a mammal and dogfish is a type of fish (specifically a cartilaginous fish).

2. **Understand the Options**:
- **Option A**: Solid single-stranded central nervous system (CNS).
- **Option B**: Lays eggs and guards them until they hatch.
- **Option C**: Possesses a bony skeleton.
- **Option D**: Have gill slits at some stages.

3. **Analyze Each Option**:
- **Option A**: The central nervous system in chordates is hollow, not solid. Therefore, this option is incorrect.
- **Option B**: Crocodiles and penguins lay eggs, but whales do not; they are viviparous (give live birth). Thus, this option is also incorrect.
- **Option C**: Dogfish have a cartilaginous skeleton (not bony), while crocodiles and penguins have bony skeletons. Therefore, this option is incorrect.
- **Option D**: All these animals (crocodiles, penguins, whales, and dogfish) have gill slits at some stage in their life cycle. This is a characteristic feature of chordates.

4. **Conclusion**:
- The correct answer is **Option D**: They have gill slits at some stages.

### Final Answer:
Crocodile and penguin are similar to whale and dogfish in that they **have gill slits at some stages**.

---