Final answer:
Cilia are short and numerous hair-like structures that aid in cellular movement or movement of substances along the surface, whereas flagella are longer and less numerous, aiding in propelling a cell. Cells with cilia typically have many, while cells with flagella usually have just one or a few. Therefore, the most appropriate correct option is B.
Step-by-step explanation:
The correct statement with respect to flagella and cilia is that cilia generate a force parallel to the cell surface. However, there are further differences to note between these two structures. Cilia are short, numerous, hair-like structures that extend from the plasma membrane and are primarily seen moving substances along the cell surface or aiding cellular movement. In contrast, flagella are longer and usually fewer in number when present on a cell. They extend from the plasma membrane and are primarily responsible for propelling a cell through its environment, as seen in sperm cells or certain eukaryotic microorganisms like Euglena. Cells generally have many cilia if they have any, while they typically have only one or a few flagella. Moreover, cilia can move in a synchronized, sweeping motion that is different from the undulating wave-like motion of flagella.