A trait is found in all mammals -

Options

A. Hair
B. Mammary glands
C. 4 chambered heart
D. All

Answer

### Step-by-Step Solution:

1. **Understanding Mammals**:
- Mammals belong to the phylum Chordata and include a diverse range of animals such as humans, cows, cats, and dogs.

2. **Identifying Common Traits**:
- One of the defining characteristics of mammals is the presence of hair or fur. This trait is found in all mammals, providing insulation and protection.

3. **Mammary Glands**:
- Another key trait of mammals is the presence of mammary glands. These glands are responsible for producing milk in female mammals to nourish their young. While all mammals have mammary glands, they are typically more developed and functional in females.

4. **Heart Structure**:
- Mammals possess a four-chambered heart, which consists of two atria and two ventricles. This structure allows for efficient separation of oxygenated and deoxygenated blood, ensuring that oxygen-rich blood is delivered to the body without mixing with oxygen-poor blood.

5. **Conclusion**:
- The traits that are found in all mammals include the presence of hair, mammary glands, and a four-chambered heart. These features distinguish mammals from other animal groups.