Answer:
Option B, Fimbriae are usually shorter than flagella whereas pili are involved in genetic exchange.
Step-by-step explanation:
Fimbriae are a structure that allows a cell to stick to any surface while flagella are locomotors that allow an organism to move. Due to functional difference, fimbriae are short in length and are more numerous. A pili is a structure that comes out of the cell and hence attaches the cell to the specific surfaces. It also assists in transferring DNAs in cell. Hami are external structures found in archae only.
Hence, option B is correct