Select the correct statement about the uterine cycle.

• A. During the secretory phase, estrogen levels are at their highest.
• B. During the proliferative phase, levels of progesterone rise as the follicle begins to produce more hormone.
• C. If fertilization occurs, the corpus luteum is maintained by a hormone secreted by the developing embryo.
• D. The menstrual phase of the cycle is from day 1 to day 8.