The correct option is C 14th day
The hormone estradiol suppresses the secretion of luteinizing hormone (LH) during the follicular phase. When the egg has almost matured, the levels of estradiol becomes maximum and beyond the optimum level, this effect is reversed and estrogen stimulates the production of large amounts of LH. This process is known as LH-surge and it starts around day 13th of the average 28- day cycle and may last for 24 - 48 hours
So, the correct answer is '14th'