Suggest why abstaining from sexual intercourse from day 9 to 19 of thiswoman’s menstrual cycle could avoid pregnancy.

The menstrual cycle of a woman typically lasts about 28 days, although it can vary. The cycle includes several phases: the menstrual phase (day 1-5), the follicular phase (day 1-13), ovulation (day 14), the luteal phase (day 15-28), and premenstrual phase (day 26-28).

1. The first day of a woman's period is considered day 1 of the menstrual cycle. During the menstrual phase, the lining of the uterus is shed through the vagina.

2. The follicular phase overlaps with the menstrual phase for a few days. During this phase, the pituitary gland releases a hormone that stimulates the ovaries to produce around 5 to 20 small sacs called follicles. Each follicle contains an egg.

3. Around day 14 of the cycle, a surge in luteinizing hormone causes the most mature follicle to burst and release an egg. This is known as ovulation.

4. After ovulation, the egg is available to be fertilized by sperm for about 12 to 24 hours. However, sperm can survive in the woman's body for up to 5 days. Therefore, if a woman has sex up to 5 days before ovulation or within a day after, she can become pregnant.

5. The luteal phase is a period of time when the body prepares for a possible pregnancy. If the egg is not fertilized, it will be shed along with the lining of the uterus at the end of the luteal phase, marking the start of a new menstrual cycle.

Abstaining from sexual intercourse from day 9 to 19 of the menstrual cycle could avoid pregnancy because this period includes the 5 days leading up to ovulation, the day of ovulation itself, and a few days after. This is the time when a woman is most fertile and therefore most likely to become pregnant if she has sex.