Final answer:
The central tubes or sheath connected to A tubules are linked by a set of microtubules, which are components of the cell's cytoskeleton.
Step-by-step explanation:
The central tubes or central sheath connected to A tubules in muscle cells are linked by a set of proteins. These proteins are part of the cytoskeleton, which provides structure and support to the cell. The options provided suggest different components of the cytoskeletal network, but based on the context of the question and the related reference material, it is clear that the correct answer is microtubules. The cytoskeletal fibers involved in various cellular functions vary, with microtubules being the thickest and involved in maintaining cell shape and organization, whereas intermediate filaments are important for resisting tension and microfilaments are involved in muscle contraction.