Which characters are found only in mammals?

Options

A. pinna, teeth
B. hair, oviparous
C. mammary glands, teeth
D. hair, mammary glands

Answer

### Step-by-Step Solution:

1. **Definition of Mammals**: Mammals are a class of vertebrates characterized by specific features that distinguish them from other animal classes.

2. **Mammary Glands**: One of the most defining characteristics of mammals is the presence of mammary glands. These glands are responsible for producing milk to nourish their young.

3. **Viviparous Reproduction**: Most mammals give birth to live young (viviparous), as opposed to laying eggs. However, there are exceptions like the monotremes (e.g., echidna and platypus) that lay eggs.

4. **Body Covering**: Mammals have skin that is typically covered with hair or fur. This is a unique feature that helps in temperature regulation and protection.

5. **Glands**: Mammals possess specialized glands, including sweat glands (for thermoregulation) and sebaceous glands (which secrete oils to keep the skin and hair healthy).

6. **Heart Structure**: Mammals have a four-chambered heart, which allows for efficient separation of oxygenated and deoxygenated blood.

7. **Respiration**: All mammals breathe through lungs, which is a characteristic feature of this class.

8. **Teeth and Ears**: Mammals have differentiated teeth (though teeth are not exclusive to mammals) and an outer ear structure known as the pinna, which helps in sound localization.

9. **Unique Characteristics**: The two characteristics that are found exclusively in mammals are:
- Presence of mammary glands
- Body hair

### Conclusion:
The unique characteristics found only in mammals are **hair and mammary glands**.

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