Flightless birds lack

Options

A. Wings
B. Keel in Sternum
C. Both A and B
D. Feathers

Answer

### Step-by-Step Solution:

1. **Understanding Flightless Birds**:
- Flightless birds are species that, as the name suggests, cannot fly. This inability to fly can be attributed to various anatomical adaptations.

2. **Wings**:
- Many flightless birds have either reduced or rudimentary wings. In some cases, such as the ostrich, wings are completely absent. In others, like the penguin, wings have been modified into flippers, which are not suitable for flight.

3. **Sternum and Keel**:
- The sternum in flightless birds is typically flat or raft-like. This is significant because the keel, which is a prominent ridge on the sternum that provides an anchor for the flight muscles, is absent in these birds. The absence of the keel is a critical factor that contributes to their inability to fly.

4. **Analyzing the Options**:
- **Option A (Wings)**: Flightless birds lack functional wings, making this option correct.
- **Option B (Keel and Sternum)**: Since flightless birds lack a keel, this option is also correct.
- **Option C (Both A and B)**: Since both wings and keel are absent in flightless birds, this option is correct as well.
- **Option D (Feathers)**: This option is incorrect because all birds, including flightless ones, possess feathers, which are a defining characteristic of the class Aves.

5. **Conclusion**:
- The most appropriate answer is **Option C (Both A and B)**, as flightless birds lack both functional wings and a keel.