The character which differentiates mammals from birds is

Options

A. Seven cervical vertebrae in neck
B. Parental care
C. One aortic arch
D. Metanephric kidney

Answer

To determine the character that differentiates mammals from birds, we will analyze the provided options step by step.

### Step-by-Step Solution:

1. **Understanding Cervical Vertebrae**:
- Mammals typically have **7 cervical vertebrae** in their neck region, which are designated as C1 to C7.
- Birds, on the other hand, can have a varying number of cervical vertebrae, usually ranging from **13 to 25**.

**Conclusion**: The number of cervical vertebrae is a key distinguishing feature, as mammals have 7 while birds have many more.

2. **Evaluating Parental Care**:
- Both mammals and birds exhibit **parental care**. This behavior is common in both groups, where typically the female takes care of the young.

**Conclusion**: This option does not differentiate mammals from birds, as both exhibit parental care.

3. **Assessing Aortic Arc**:
- Both mammals and birds possess **one aortic arc** in their circulatory system.

**Conclusion**: This characteristic is the same for both groups and does not serve as a differentiating factor.

4. **Examining Metanephric Kidney**:
- The term **metanephric kidney** refers to a fully developed and functional kidney. Both mammals and birds possess this type of kidney.

**Conclusion**: This characteristic is also not unique to either group, as both have metanephric kidneys.

### Final Answer:
The character which differentiates mammals from birds is the presence of **7 cervical vertebrae** in mammals, while birds have **13 to 25 cervical vertebrae**.

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