Suddenly, my daughter went to school. On the first day of school, when I was carrying my daughter's schoolbag, her daughter complained, "It's so heavy!" I froze for a while and picked up my daughter's schoolbag. It's really heavy I didn't expect students to be under so much pressure now. After seeing my daughter off, I went to the laboratory to study. After a day's research, I invented a "burden-reducing schoolbag".