Final answer:
Microtubules are characterized as hollow tubes made of α-tubulin and β-tubulin dimers, playing crucial roles in cell structure, movement and division.
Step-by-step explanation:
Microtubules are a component of the cytoskeleton and are best characterized as C. hollow tubes. They are made up of polymerized dimers of α-tubulin and β-tubulin. These hollow structures have a diameter of about 25 nm and are involved in various cellular functions. Microtubules provide structural support, resist compression, facilitate organelle and vesicle movement with the help of motor proteins such as dynein and kinesin, and are crucial during cell division by helping to segregate chromosomes. They are also critical components of eukaryotic flagella and cilia.