Which one of the following hormones attains the highest concentration during the postovulatory phase of the menstrual cycle?

Progesterone level peaks around 21st day of a 28-day menstrual cycle. Oestrogen is also secreted by the corpus luteum during the luteal (postovulatory) phase, but its level is lower than that of progesterone. FSH and LH levels are low during the luteal phase.