Explanation:

After ovulation, the follicle transforms into the corpus luteum, which secretes progesterone. The hormone levels change during the menstrual cycle, and the levels of hormones are different in different phases of the menstrual cycle. In the post-ovulatory phase, the hormone levels change as follows:

LH:

The luteinizing hormone (LH) is responsible for ovulation, and it peaks just before ovulation. After ovulation, the LH level drops and remains low in the post-ovulatory phase.

FSH:

The follicle-stimulating hormone (FSH) is responsible for the growth of the follicle and the production of estrogen. After ovulation, the FSH level drops and remains low in the post-ovulatory phase.

Progesterone:

After ovulation, the corpus luteum produces progesterone, which prepares the uterus for pregnancy. The level of progesterone increases after ovulation and remains high in the post-ovulatory phase.

Estrogen:

Estrogen is produced by the follicle and is responsible for the growth of the endometrium. After ovulation, the estrogen level drops and remains low in the post-ovulatory phase.

Therefore, the hormone level that is least in the post-ovulatory phase is FSH, as it is responsible for the growth of the follicle and the production of estrogen, which are both decreased after ovulation.