Which one of the following is a flightless bird ?

Options

A. Emu
B. Duck
C. Peacock
D. Sparrow

Explanation

To determine which one of the following is a flightless bird, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Characteristics of Flightless Birds**:
- Flightless birds are species that have lost the ability to fly. This is often due to evolutionary adaptations to their environment.

2. **Identify the Key Structure for Flight**:
- The ability to fly in birds is primarily supported by a structure called the keel. The keel is an extension of the breastbone (sternum) that provides an anchor for the pectoral muscles, which are crucial for wing movement.

3. **Recognize Examples of Flightless Birds**:
- Common examples of flightless birds include the Emu, Kiwi, and Ostrich. These birds lack a keel, which prevents them from flying.

4. **Evaluate the Options Provided**:
- If the options include Emu, Kiwi, Ostrich, or other birds, we can analyze them based on their ability to fly.

5. **Select the Correct Answer**:
- Among the options, if "Emu" is listed, it is confirmed to be a flightless bird as it does not have a keel and cannot support its body weight with its wings.

### Conclusion:
- The correct answer is **Emu** (Option A), as it is a flightless bird.