8. Vinblastine is a standard chemotherapeutic drug used to treat cancer. Because it interferes with the assembly of microtubules, its effectiveness must be related to (A) myosin denaturation and inhibition of cleavage furrow formation. (B) disruption of mitotic spindle formation. (C) inhibition of DNA synthesis. (D) inhibition of regulatory protein phosphorylation. (E) suppression of cyclin production.