Final answer:
Microtubules are essential components of cilia, which is option A. They are important for cell structure, division, and movement.
Step-by-step explanation:
Microtubules are essential components of cilia, so the correct answer is A. cilia.
Microtubules are cytoskeletal structures that play a critical role in cell shape, cell division, and the movement of organelles within the cell. They are composed of polymers of the protein tubulin. In eukaryotic cells, microtubules are integral to the structure and function of cilia and flagella, which are involved in cell motility and sensory functions. Microtubules also form the spindle fibers that are essential during cell division, specifically mitosis and meiosis, which polymerize from centrioles. The centrosome, present in animal cells, serves as the microtubule-organizing center (MTOC).
In contrast, structures like the nucleus, nucleolus, cell membrane, and peroxisomes do not primarily use microtubules as their structural components. Therefore, for the given options, cilia are the correct choice linked directly to the role of microtubules.