5. Some cytoskeletal fibers are formed from globular protein subunits. This type of fiber includes the (A) Intermediate filaments and actin microfilaments. (B) Thick and thin filaments of skeletal muscle. (C) Microtubules and the thick filaments of skeletal muscle. (D) Keratin filaments in the skin and the thick filaments of skeletal muscle. (E) Actin microfilaments and microtubules.