Long bones of birds are

Options

A. not ossified
B. pneumatic
C. cartilaginous
D. totally solid

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the nature of long bones in birds. We need to identify their characteristics.

2. **Identifying the Class of Birds**: Birds belong to the class Aves. This classification is important because it helps us understand the adaptations that birds have developed for flight.

3. **Analyzing Bone Structure**: The long bones of birds are adapted for flight. One key adaptation is that they are lightweight. This is crucial for birds as it allows them to fly efficiently.

4. **Understanding Bone Composition**: The lightweight nature of bird bones is due to their internal structure. Unlike human bones, which are dense and filled with a matrix and fluid, bird bones have internal spaces that are filled with air.

5. **Defining Pneumatic Bones**: The bones that contain air-filled spaces are known as pneumatic bones. This structure significantly reduces the overall weight of the bird, aiding in flight.

6. **Choosing the Correct Answer**: Given the options provided in the question, the correct answer is that the long bones of birds are "pneumatic."

### Final Answer:
The long bones of birds are pneumatic.

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