Which of following characteristic features always holds true for corresponding group of animals

Options

A. Cartilaginous : Chondrichthyes
B. Viviparous : Mammalia
C. Possess a mouth with an upper and a lower jaw : Chordata
D. 3- chambered heart with one incompletely divided ventricle : Reptilia

Answer

To solve the question regarding which characteristic features always hold true for the corresponding group of animals, we can analyze each option step by step.

### Step-by-Step Solution:

1. **Option A: Cartilaginous (Chondrichthyes)**
- Chondrichthyes refers to a class of fishes that have a skeleton made of cartilage instead of bone.
- This characteristic is consistent and holds true for all members of this group.
- **Conclusion**: This option is correct.

2. **Option B: Viviparous (Mammals)**
- Viviparous refers to the reproductive method where animals give birth to live young.
- While most mammals are viviparous, there are exceptions such as the platypus, which is oviparous (lays eggs).
- **Conclusion**: This option is incorrect due to exceptions.

3. **Option C: Caudata (Chordata)**
- Caudata refers to a class of amphibians (like salamanders) within the phylum Chordata.
- The statement about having a mouth with upper and lower jaws does not hold true for all chordates, as there are many variations in jaw structure across different groups.
- **Conclusion**: This option is incorrect.

4. **Option D: Reptiles with a Three-Chambered Heart**
- It is generally true that most reptiles have a three-chambered heart.
- However, crocodiles, which are also reptiles, possess a four-chambered heart, making this statement not universally applicable.
- **Conclusion**: This option is incorrect.

### Final Answer:
The characteristic feature that always holds true for the corresponding group of animals is **Option A: Cartilaginous (Chondrichthyes)**.

---