In the 13th century, the famous Italian traveler, Marco Polo, traveled to China. During his stay in China, he discovered ____ the Chinese used paper money. In western countries, people didn't use paper money ____ 15th century. ____, people in China began to use paper money in the 7th century. A Chinese man called Cai Lun ____ paper about 2 000 years ago. He put these pieces of paper together and made them into a book.

    We use a lot of paper every day. If we keep on ____so much paper, there will be no paper. So how can we save paper? We can use ____sides of every piece of paper. We can choose drinks in bottles ____of those in paper packets(小包). We can ____ use handkerchiefs(手帕) and not paper ones. When we go shopping we can use fewer paper bags. ____ the shop assistant gives you a paper bag, we can save it and reuse it later.

    ____ has the duty to help to save paper. We should do it now, before it is too late.