The correct option is B Days 10-17
Ovulation occurs somewhere between the 13th and 15th day before menses and the sperm can live up to 3 days in the vagina, which means the first unsafe day will be the 10th day. And ovulation can occur as late as the 16th day and the ovum is receptive to fertilization for about 24 hours, so the final unsafe day is day 17. As menstrual cycles may vary in length by 3 to 5 days, abstinence from the 10th to the 17th day of a woman’s menstrual cycle is recommended.