The correct option is D All of the above
The cytoskeletal structures are of three types - microtubules, microfilaments and intermediate fibres. Microtubules were discovered by DeRobertis and Franchi (1953) in nerve axons and named as neurotubules. The term Microtubules was coined by Slautterback in 1963. Microtubules are basic structures of spindle apparatus, centrioles, basal bodies, cilia and flagella. They are also present in other cellular structures like sensory hairs, nerve processes, sperm tail etc. Microtubules present in cytoplasm provide shape and polarity to cells. They are involved in cell movements along with microfilaments, chromosome movements and intracellular transport.