Final answer:
Option d.
The intermediate filaments within the cytoskeleton are the least dynamic and serve primarily structural roles, unlike microtubules and microfilaments, which disassemble and reform quickly. The correct option is 'd. only intermediate filaments'.
Step-by-step explanation:
Of the cytoskeletal protein elements including microfilaments, intermediate filaments, and microtubules, the most stable and least dynamic are the intermediate filaments.
Microfilaments, made primarily of actin, and microtubules, composed of tubulin, are both involved in maintaining cell shape and facilitating cellular movements and are dynamic in nature, assembling and disassembling as needed.
In contrast, intermediate filaments provide structural support and bear tension, resisting forces that pull apart cells but are not known to be dynamic.
Therefore, intermediate filaments serve mainly structural roles in cells and do not rapidly disassemble and reassemble like microtubules and microfilaments.
The correct option to this question is d. only intermediate filaments, which are not dynamic like the other cytoskeletal filaments.