Sternum Is kneeled in :-

Options

A. Amphibians & Reptiles
B. Birds & Bats
C. Reptiles & Mammals
D. All of these.

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which group of animals has a sternum that is "nailed in" or "keel-shaped."

2. **Analyzing the Options**:
- **Option 1: Amphibians and Reptiles**: These groups do not have a keel-shaped sternum. The sternum in these animals is generally flat and does not support flight muscles.
- **Option 2: Birds and Bats**: Birds have a specialized sternum known as a keel, which is an extension of the breastbone. This keel provides an attachment point for the powerful flight muscles, making it essential for flight. Bats, being mammals, also have a similar structure but are not primarily classified with birds in this context.
- **Option 3: Reptiles and Mammals**: Similar to option 1, reptiles do not have a keel-shaped sternum. Mammals, while they have a sternum, do not have a keel structure like birds.

3. **Identifying the Correct Answer**: Based on the analysis, the correct answer is **Option 2: Birds and Bats**, as they possess a keel-shaped sternum.

4. **Conclusion**: The sternum is "nailed in" or keel-shaped primarily in birds, which aids in their flight capabilities.