For Approximately How Long During the Human Female's Menstrual Cycle

For approximately how long during the human female's menstrual cycle are progesterone concentrations high enough to maintain the uterus in a proper condition for pregnancy?

A) The entire duration of the cycle
B) No portion of the cycle
C) During the first half of the cycle
D) During the second half of the cycle
E) For a 5-day window mid-cycle