PART A
The best response to fill in the chart for "B" would be: B. 23 chromosomes
This is because "B" likely refers to the number of chromosomes in human gametes (sperm and eggs), which is half of the usual diploid number of chromosomes (46).
PART B
The best description of why your answer in Part A must occur every time is: C. Mitosis forms sperm and eggs which must have half the number of chromosomes as the original.
This is accurate because during meiosis (not mitosis) the number of chromosomes is halved to produce gametes, ensuring that when sperm and egg unite during fertilization, the resulting zygote has the correct diploid number of chromosomes.
If you meant to reference the formation of gametes specifically, meiosis is the correct process rather than mitosis. If the context was just overall cell division and maintaining chromosome number in somatic cells, then D would be appropriate for those scenarios.