What is the main locomotory structure of bacteria?

Bacteria are prokaryotic microorganisms, and many species possess specialized structures for movement within their environment.

• Flagellum (B) is correct. A flagellum (plural: flagella) is a whip-like appendage that protrudes from the cell body of certain prokaryotic and eukaryotic cells, primarily serving as a means of locomotion. Many bacteria use flagella to propel themselves through liquid environments.
• Pseudopodia (C) is incorrect. Pseudopodia ("false feet") are temporary extensions of the cytoplasm used for locomotion and feeding by some eukaryotic cells, like amoebas, not typically bacteria.
• Options A and D are empty and therefore incorrect.