题目

In the 13th century,the famous Italian traveler,Marco Polo,traveled a long way to China.During his stay in China,he saw many wonderful things.One of the things he discovered was that the Chinese used paper money.In western countries,people did not use paper money until the 15th century.However,people in China began to use paper money in the 7th century.A Chinese man called Cai Lun invented paper almost 2,000 years ago.He made it from wood.He took the wood from trees and made it into paper.He then put these pieces of paper together and made them into a book.Now paper still comes from trees.We use a lot of paper every day.If we keep on wasting so much paper,there will not be any trees left on the earth.If there are no trees,there will be no paper.Every day,people throw away about 2,800 tons of paper in our city.It takes 17 trees to make one ton of paper.This means that we are cutting nearly 48,000 trees every day.Since it takes more than 10 years for a tree to grow,we must start using le

提问时间：2020-10-08

答案

Saving paper
前面的历史是铺垫.给后面保护树木节约用纸的铺垫