The role of progesterone is not stimulating ovulation. The meaning of ovulation is the release of egg from the ovaries and it occurs when the follicles rupture and release the secondary oocyte ovarian cell.
So, the option (a) is incorrect answer.
The role of progesterone is also not the conversion of folic acid into corpus as it is the work of the intestines that follow the digestive process.
So, the option (b) is incorrect answer.
The role of progesterone is also not the start of the periods or menstruation.
So, the option (d) is also incorrect.
The role of progesterone in the female reproductive system is that it stimulates the development of the endometrium. If the ovum is fertilized, embryo will implant itself into the endometrium and begin to form an amniotic cavity, umbilical cord, and placenta.
So, the option (a) is the correct answer.