Final answer:
Two tubular profilaments form a spindle that makes up the mitotic spindle. The alpha and beta tubulin dimers of microtubules are essential for this process, particularly during cellular division.
Step-by-step explanation:
Two tubular profilaments make a spindle, and these make up the mitotic spindle. The correct answer to the student's question is a) Spindle; mitotic spindle. Microtubules, composed of alpha and beta tubulin dimers, radiate from the centrosome near the nucleus and help the cell maintain its shape, hold organelles in place, allow organelle movement, and are crucial for the assembly of the mitotic spindle during cell division. Moreover, microtubules are an integral part of cilia and flagella needed for cell motility.