The motile bacteria are also to move by

Options

A. Fimbriae
B. Flagella
C. Cilia
D. Pili

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about how motile bacteria move. We need to evaluate the options provided: fimbri, flagella, cilia, and pili.

2. **Analyzing Each Option**:
- **Fimbri**: These are hair-like structures that help bacteria adhere to surfaces, particularly animal cells. They do not play a significant role in movement.
- **Flagella**: These are whip-like appendages that are crucial for locomotion in bacteria. They are helical in shape and made of a protein called flagellin. Flagella enable bacteria to swim and move towards or away from stimuli.
- **Cilia**: These are short, hair-like structures that provide locomotion primarily in protozoa, not in bacteria.
- **Pili**: These are also hair-like structures but are primarily involved in adherence to surfaces and facilitating infection rather than movement.

3. **Identifying the Correct Answer**: After analyzing all the options, the most appropriate structure that allows motile bacteria to move is **flagella**.

4. **Conclusion**: The correct answer to the question is **flagella** (option B).