Final answer:
Preventing the formation of spindle fibers would most likely halt mitotic division at metaphase, as spindle fibers are crucial for chromosome alignment and separation.
Step-by-step explanation:
If spindle fibers are prevented from forming, the most likely result is that mitotic division stops in metaphase and cannot proceed to anaphase. This happens because spindle fibers play a critical role in aligning chromosomes during metaphase and then in separating sister chromatids during anaphase. In their absence, chromosomes would not be able to properly align or separate, which is essential for cell division. Therefore, the correct answer to this question is D.