Many American schools have been closed for summer. Most chil-dren in the United States have a sum-mer holiday for almost three months. This traditional school schedule was designed long ago when many Ameri-cans lived on farms. Children were needed at home during the summer to help their families with crops and ani-mals. Schools later continued the tra-dition, mostly because it was difficult to hold classes in hot summer weath-er. 全文查看链接