Final answer:
The correct answer is 'b. cilia fibers,' which do not form part of the mitotic spindle structure; the mitotic spindle includes interpolar, astral, and k-fibers.
Step-by-step explanation:
The types of microtubules found in a mitotic spindle include interpolar fibers, astral fibers, and k-fibers (kinetochore microtubules). The answer to the question is 'b. cilia fibers', as cilia are not part of the mitotic spindle structure. Interpolar fibers are also known as polar microtubules and contribute to cell elongation during mitosis. Astral microtubules are located near the poles and are required for the regulation of mitosis. Kinetochore microtubules attach to the kinetochore of chromosomes and assist in their movement. The term 'ip-fibers' is not a standard term used to describe any of the spindle fibers, but it is not explicitly listed as an incorrect answer as 'cilia fibers' are.