Correct Option: B

Microtubules are long, hollow cylinders made up of polymerised a- and b-tubulin dimers. Microtubules are part of a structural network (the cytoskeleton) within the cell’s cytoplasm. Roles of the microtubule cytoskeleton include mechanical support, organization of the cytoplasm, transport, motility and chromosome segregation so they are present in cilia and flagella for cellular movement, centrioles for chromosomal movement and spindle fibres for structural organization as well as chromosomal movement during nuclear division.