A、To mix pulp with water. B、To keep the shape and thickness of the paper. C、To keep the paper strong enough. D、To dry the paper

The earliest process of making paper was done almost 5 000 years ago in Egypt.(16)In those days, paper was made from strips of a special plant. Modern paper-making began in China about 2 000 years ago. At that time, paper was made from cloth, straw, wood or the bark of trees. Large machines started to be used for making paper near the end of the 16th century. Today, paper-making is a big business. But it’s still possible to make paper by hand, since the steps are the same as using big machines.(17)You should choose paper with small amounts of printing. Old envelopes are good for this reason. Colored paper also can be used, as well as small amounts of newspaper. Small pieces of rags or cloth can be added. They should be cut into pieces about five centimeters by five centimeters. Everything is placed in a container, covered with water and brought to the boil. It is mixed for about two hours with some common chemicals and then allowed to cool. Then it’s left until most of the water dries up. The substance left, called pulp, can be stored until you’re ready to make paper. When you’re ready, the pulp is mixed with water again.(18)Then the pulp is poured into a mold. The mold is made of small squares of wire that hold the shape and thickness of the paper. To help dry the paper, the mold lets the water flow through the small wire squares. After several more drying steps, the paper is carefully lifted back from the mold. It’s now strong enough to be touched.
16. Which of the following is used in the earliest paper-making?
17. What is the most ideal material for making paper by hand?
18. What is the purpose of a mold in making paper?
19. What does the passage mainly tell us?