Bacterial flagella have a very complex structure composed of 42 distinct proteins. What is the most likely explanation for the evolution of these complex structures?

• A. Genes for eukaryotic flagella were taken up and expressed in bacteria.
• B. Endosymbiosis added flagella to prokaryotes.
• C. Early bacterial species needed to be able to move and thus developed complex flagella to facilitate this motility.
• D. Flagella evolved as extensions of other bacterial appendages such as pili and fimbriae.
• E. Exaptation recruited non-flagellar proteins to new functions.