Long long ago, people lived on wild animals, fruits and other plants and they didn’t need to use money.

As time passed, families had more products (产品) than they needed, such as animals and crops. So they needed to trade with others. They began to use money to make it easier. However, it was not like the money we use today. They used shells, rice, salt or large stones.

During the 600 BC, people began using coins as money. Because they were easier to carry than goods (货物), countries began to make coins as their money.

The Chinese were the first to use paper money, probably in the 11th century. An Italian traveler, Marco Polo, saw the Chinese use paper money when he visited China in the 1200s. After his travel, he told the western people what he saw. But European countries didn’t start using paper money till the1600s.

Today people have many ways to pay for things, such as coins, paper money and cards. Some prefer to pay by card. That’s because paying with a card is easier and safer than carrying around a lot of “real” money.

Whenever the word “peace” comes into our mind, we can’t help thinking of a white-coloured bird who has a leaf in its mouth. But have you ever wondered why this little bird became a symbol of peace?

It is believed that this symbol comes from the Bible. Actually, for the first time, it appeared in the story about Noah’s Ark（诺亚方舟），In the story, when the heavy rain that flooded the earth stopped pouring down, Noah sent out a white dove to see if there was any land. Then the dove returned with an olive branch（橄榄枝）in its mouth, which meant that it had found dry land somewhere. This brought hope to Noah, who had almost spent almost a year on his ark. From then on, the white dove was considered the symbol of hope and new life.

In another very popular story from Central Asia, a big war was about to happen between two kingdoms. When one of the kings asked for his helmet （头盔）he was told that a dove had made a nest into it. The king’s mother wanted him to keep the nest and the doves. The king agreed and headed for the war without his helmet. Upon seeing the king without his helmet, the other king asked the reason. The king told the truth. The other king was deeply touched by his action. And they finally agreed to make peace instead of war. A nest of doves became a reason for stopping a war. Since then, the dove has been connected with peace.

In ancient Japan, a dove carrying a sword（剑）meant the end of war. And in ancient Europe, there was a tradition that if a dove flew around a house where someone was dying, then their soul would be at peace.

Besides, many artists also regard the bird as a symbol of peace. But it was Pablo Picasso who made the white dove a popular modern symbol of peace when he used it on a poster for the World Peace Congress (WPC) in 1949.

Why do We Yawn?

Do you yawn? There are about 20 reasons that scientists think are possible for yawning after research. They do not know exactly why yawning happens, 【小题1】.

We know that everyone yawns in the same way. First you open your mouth slowly. Your mouth stays open for about five seconds. You take in a lot of air and then push it out, 【小题2】. When you see someone yawn, you yawn, too.

Many people say they yawn because they are bored or tired. That might be true. People do often yawn before they sleep and after they wake up. 【小题3】. Olympic runners, for example, often yawn before a race. Why is that? In 2007, scientists found that a yawn can help a warm brain cool down.

Some scientists believe that yawning makes you notice things more quickly. When you yawn, you breathe deeply. You also stretch (强化) the muscles (肌肉) in your face, mouth, and neck.

In some countries, people think yawning is not nice. People put their hands over their mouths to cover a yawn. 【小题4】. They think that opening the mouth very big can let good things in. When they breathe out, they think that bad things go out of the body with the air.

Scientists do not spend much time studying yawning. That is probably because yawning does not hurt. It is just something we do.