Answer: Option A
Step-by-step explanation:
Cyclin binds with an enzyme to produce MPF Cyclin, and as its concentration rises, it promotes mitosis.
Therefore, cyclin binds with a factor to produce MPF enzyme, and as the enzyme's concentration decreases, it promotes mitosis; the MPF Cyclin concentration remains constant, as the rise and fall of the MPF enzyme controls the cell cycle; the MPF Cyclin concentration increases and decreases in a cycle, but does not control the cell cycle are not best described the relationship between MPF and cell cycle.