Right option is (a) corpus luteum
To explain I would say: During the luteal or secretory phase, the Graafian follicle is ruptured and the egg is released from the ovum into the fallopian tube to encounter the sperm. The empty Graafian follicle gets filled with the external theca and granulosa cells. This is the onset of degeneration of Graafian follicle and is called the corpus luteum.