If after ovulation, pregnancy does not take place, then the corpus luteum

The correct option is degenerates in a short time.

During the luteal phase of the menstrual cycle, the ruptured Graafian follicle transforms into a temporary endocrine structure called the corpus luteum under the influence of Luteinizing Hormone (LH). The corpus luteum primarily secretes progesterone, along with small amounts of estrogen, to prepare and maintain the endometrium (uterine lining) for the implantation of a fertilized egg.

If fertilization and pregnancy do not occur, the egg is not implanted, and no Human Chorionic Gonadotropin (hCG) hormone is produced. In the absence of hCG support, the corpus luteum cannot sustain itself. Consequently, it begins to regress and degenerates in a short time (approximately 10 to 14 days after ovulation) into a non-functional, white fibrous scar tissue called the corpus albicans.

This degeneration leads to a rapid decline in progesterone and estrogen levels. The sudden withdrawal of these hormones causes the endometrium to disintegrate and shed, resulting in menstruation and marking the start of a new menstrual cycle.