What is the cell-supporting structure that consists of fibers such as actin, microtubules, and intermediate filaments?

The cytoskeleton is the correct answer because it is a dynamic network of fibers found within the cell that provides structural support, shape, and organization. It is composed of several types of protein filaments, including actin filaments, microtubules, and intermediate filaments.

Actin filaments, which are also known as microfilaments, are involved in various cellular movements and shape changes. Microtubules serve as tracks for the movement of organelles and are critical for cell division as they form the mitotic spindle. Intermediate filaments provide mechanical support and stability to the cell by anchoring organelles in place.

This network is essential for many cellular functions, including maintaining the cell's structure, facilitating intracellular transport, and enabling cell division and movement. The other structures listed, such as the endoplasmic reticulum, nucleus, and Golgi apparatus, have distinct functions related to protein synthesis, genetic material storage, and modification and secretion of proteins, respectively, but they do not play the role of providing structural support to the cell in the same way that the cytoskeleton does.