The correct option is A Corpus luteum
Corpus luteum is the temporary endocrine gland of ovary which is formed from Graafian follicle after ovulation. Ovulation is followed by rupturing of Graafian follicle with a clot inside called as corpus hemoragicum. Absorption of clot and other changes transforms it into corpus luteum which secretes estrogen and progesterone during first three months of pregnancy. Corpus luteum is maintained by human chorionic gonadotropic hormone, if pregnancy occurs. Placenta takes over the function to secrete it for next 6 months of pregnancy till parturition.