Many bacteria are motile due to the presence of:

Explanation

The correct answer is Flagella. Flagella are specialized structures that provide motility to bacteria by rotating like propellers, allowing them to move towards or away from various stimuli. This is a key feature distinguishing motile bacteria from non-motile ones. Other structures like Pili are involved in adhesion rather than movement, Cilia are not present in bacteria, and Microtubules are eukaryotic cell structures unrelated to bacterial motility.