It is well-known that silk was discovered in China. It is wonderfully strong, light and     1    . As one of the best materials for clothes, silk has a perfect look and feel that no other materials can match.

There is a story about how silk was     2    . Lei Zu, the wife of Huang Di, was having tea under a mulberry tree when a silkworm cocoon (蚕茧) fell into her cup. As she tried to take the cocoon     3    , it started to unwind (展开) and the “line” seemed endless. She realized that the strong line could be used to make     4    . Then Lei Zu taught her people how to raise silkworms and how to get silk. In this way, the silk industry was born.

For hundreds of years after that, silk was only used by rich people. It was a symbol of identity and status (身份和地位). With the development of the silk industry,     5     silk was produced. It was no longer just for rich people. In the Han Dynasty, silk was transported as far away as Spain, Rome and many other countries. The trade road was     6     known as the Silk Road, which connected China with the rest of the world.

Today, silk can be used for many kinds of things, not just for clothes but also for paintings, writing brushes, kites and even fishing nets. Wherever silk goes     7     the world, it is always warmly received.

Today, making a phone call is as common as having a glass of water. However, when telephones were invented more than 130     1     ago, people believed that they were dangerous.

In 1876, when the first telephone was shown to the public, electricity was still a     2     thing. Many people died while they worked with electricity at that time. That’s why most people thought it was unsafe to bear a human voice     3     the phone. Many people feared the phone would     4     them.

But on the morning of March 10, 1876, Alexander Bell and Thomas Watson, had no such fears. They tried to make their     5     the telephone, work. Bell sent Watson to a room in the basement (地下室). In a room upstairs, Bell spoke seven little words on the phone. These     6     words changed the world forever. “Mr. Watson, come here. I want you.” Watson heard these words clearly and     7     an upstairs to tell the good news.

The telephone was born in March 1876,     8     it took a few more years to get popular. Bell had to overcome (克服) the fears about electricity before people     9     telephones. He also had to convince (说服) people it was safe to use it.

Now we see telephones everywhere. It is hard to imagine that not so long ago, telephones were thought to be dangerous. Our     10     certainly has changed, don’t you think so?

Paper, also called zhi, was a Chinese invention. About 2,000 years ago, Chinese people     1     paper-making (造纸). At that time, zhi was made     2     silk and was very expensive. Only the emperor and rich people could afford to use     3    . About 1,900 years ago, Cai Lun improved the paper-making     4    . He made cheap zhi out of tree bark and old cloth.

The improvement in paper-making     5     zhi far and wide, and many different kinds of zhi were made by Chinese people. Xuan paper, a type of high-quality rice paper, can show the charm (魅力) of     6     Chinese painting and calligraphy best. Later, Chinese zhi spread to the West through the Silk Road. It became one of the     7     popular inventions in the world. With zhi, the cost of producing books became more affordable,     8     knowledge could be shared more widely. Chinese zhi now is     9     used around the world. Humans are full of infinite wisdom. No one knows     10     the future will be like.

Our grandparents seem to have magic powers sometimes. Give them a Chinese lunar calendar,     1     they will know what the weather will be like days or even months later.                                 

What’s the     2    ? They are following the 24 Solar Terms（节气）, which is an important part of Chinese culture. And last year, the United Nations     3     it to the list of the Intangible Cultural Heritage of Humanity（人类非物质文化遗产）.

The 24 Solar Terms began during the ancient periods. At that time, most Chinese people made     4     living on farms. So, weather changes were     5    . But of course, they had no satellite, Internet or weather broadcast to help them.

But people found a way. They studied the sun’s movement and also     6     attention to other natural changes     7     air temperature, water and crop growth. In the end, they worked out 24 solar terms to mark the changes.

The terms became their guide to farming work. For example, the solar term jingzhe（惊蛰）is when insects wake up     8     a long sleep in the cold winter. Farmers take it as a     9     of warm weather and get busy working.

The 24 Solar Terms is regarded as China’s     10     great invention, after paper-making, printing, the compass and gunpowder. Now, it is still used in daily life.

Chinese people have used wind     1     for thousands of years. Because of the need of war, Zhang Liang invented the kite. To send messages, Zhuge Kongming invented the sky lantern. To go     2     to do business with foreigners, Zheng He used wind to drive his big ships.

Wind power is a clean     3     of energy. Now we use it to make electricity mainly. Wind makes windmills spin (风车旋转) .When the windmills spin, they make electricity. It is said that there are     4     of windmills in the world now. Why is wind power so popular? First, it’s clean. Windmills don’t     5     the environment at all. Second, we can use wind power forever (永久) because there is always wind in nature.

Some people are afraid that windmills will kill birds. It     6     to be true, but it isn’t true anymore. Old windmills killed birds because they spun very fast. New windmills spin slowly, and they aren’t dangerous for birds. Some people say building windmills will be     7     to the environment. There is no need to worry about it. As long as (只要) we choose the right places, they won’t     8     the environment around. Also, windmills are always in unfrequented (人烟稀少的) places, so their noises can’t     9     us at all.

Wind power is becoming more and more common. So     10    , more than 80 countries have used wind power to make electricity. About 2.5 percent of the world’s power comes from the wind.

Robots don’t seem new to people now. And they have a long     1    . The first robot was made by a Greek inventor. You may see robots in some     2    . The robots in these films are stronger, faster and     3     than people. In real life, most robots are used in factories. They are used to do many     4    , difficult or dangerous jobs. Some people can’t look     5     themselves and robots are used to help them. For example,     6     some people can’t see, they can use a dog to help themselves move around. This dog is     7     a guide dog. Scientists are trying to make a robot to help them. In the future, a robot dog may take the place of a guide dog.

Robots are also used in American hospitals. At a hospital, a robot     8     meals from the kitchen to the patients’rooms. It never loses     9     way because it has a map of the hospital in its computer system.

In the future, robots     10     can help us in different ways will work in space. But they will never take the place of humans.