Which one of the following features does not belong to mammals?

Options

A. They have a backbone
B. They are cold-blooded animals
C. They have their body covered with fur or hair
D. They can produce milk to feed their young ones

Answer

To determine which feature does not belong to mammals, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Identify the Features of Mammals**:
- Mammals are characterized by certain features that distinguish them from other animal groups.

2. **Feature 1: They have a backbone**:
- This statement is correct. All mammals, including humans, have a backbone (vertebral column) as they belong to the phylum Chordata.

3. **Feature 2: They are cold-blooded animals**:
- This statement is incorrect. Mammals are warm-blooded (endothermic), meaning they can regulate their body temperature internally, regardless of the external environment. Cold-blooded animals (ectothermic) include fish and reptiles.

4. **Feature 3: They have their body covered with fur or hair**:
- This statement is correct. Mammals typically have hair or fur on their bodies, which helps in insulation and protection.

5. **Feature 4: They can produce milk to feed their young ones**:
- This statement is also correct. One of the defining characteristics of mammals is that they possess mammary glands that produce milk to nourish their offspring.

6. **Conclusion**:
- The feature that does not belong to mammals is "They are cold-blooded animals."

### Final Answer:
The feature that does not belong to mammals is: **They are cold-blooded animals.**