Toward the end of puberty, girls start to release eggs every month which is called the mensural cycle.
Around 1 or two times in a month, during ovulation which is the release of eggs, an ovary takes a tiny eggs and puts/sends it into one of the fallopian tubes where the fertilization occurs.
The egg tends to dry up fairly quickly which usually happens in around 14 days unless of course it's fertilized by sperm.
When the egg leaves the body, this specific process is menstruation (also known as her "period") and is completely normal for girls to have.
Blood and tissue from the uterus join together for the mensural flow which can be a different number of days depending on who you are, but it usually last 3-6 days.
It is impossible to avoid thinking about alcohol, as friends will bring it up to you. If you do avoid thinking about alcohol, you will not be prepared to come up with valid excuses to turn down alcohol, and may succumb to peer pressure.
Pretending to drink will land you in the wrong crowd of people who actually do drink. The crowd may offer you actual alcoholic drinks that you will be pressured to drink, or you will risk being outed as a pretender.
Hanging out with peers who drink will make drinking seem more normal as you hang out with them more.
The best way to resist the peer pressure to drink is to think of reasons for not drinking. This way, you can prepare yourself by thinking of good answers and reasons for not drinking ahead of time and convince your friends to not pressure you into drinking.
The middle one is the answer
