1. Primary school: This is the simplest and most direct period of trust and dependence between people. The friendship between pupils and friends is pure, caring and interdependent, and this simple friendship will be cherished forever.

2. Junior high school: Junior high school is the first turning point in life, and the arrival of adolescence has brought great changes to both physiology and psychology. At this time, communication and support with friends will become a very important reliance. The closest friends in this period are often bosom friends and will always be cherished.

3. High school: The study pressure in high school and the confusion in the future also need the support of friends. Friends who spent high school with themselves will witness many firsts in their lives and have deep fetters. This friendship will be treasured for a long time.

4. University period: University is the most important four years in life growth. Studying life with classmates and experiencing many firsts in life together have the highest gold content. The best friend in college is often a lifelong confidant and the most precious wealth in life.

Therefore, the friendship in every stage of life is equally precious, but the friendship in primary school, junior high school, senior high school and university is extremely precious because students have spent many important periods in their personal growth together and witnessed many firsts in life. Even after many years, the reunion with these old friends can still touch the deepest string in my heart.

This is why we often remember and cherish our old friends from our school days. Those who walked through those days together will leave the deepest impression in their memories. This may be the mystery of the emotion between people.