How do animals communicate (交流) with each other? They have special “languages”. In fact, they are using signals (信号). Different signals have different meanings.

For example, when a bee (蜜蜂) finds food somewhere, it flies home quickly. It can’t speak, but it can tell others by dancing. Other bees will know where and how far the food is.

Some animals show their feelings by making sounds. For example, when a dog is angry, it barks (吠). At this time, you’d better stay away from it. Birds can make several sounds to show different meanings. Sometimes we humans show feelings by making sounds instead of by speaking. For example, when we feel painful (疼痛的), we cry“Oh!”or“Ouch!”.

We humans have languages and words. We can communicate face to face by speaking. We can write down what happened in order to remember clearly. We can also send (寄) messages to people far away. But animals can’t.   

根据短文内容，判断句子正误。正确的用A表示，不正确的用B表示。

What subject do you worry about the most at school? Many student worry about math. Some student can’t sleep well the day before a math exam. Others may feel very nervous during the math exam. But do you know the right postures might be a way to make you less nervous?

Postures mean the ways you sit in front of your desk. When you study, maybe you changes your postures all the time. Sometimes you slump over or sit up straight. Or sometimes you lie on your back or put your head on your desk.

For those students who feel like a deer in the headlights before taking a math test, a simple change in posture could make a big difference.

Scientists have tested 125 college students. They ask the students to do a sample math test while sitting in a slumped over position ,or sitting up straight. After the test, 56% of students say the exam is easier to do if they are sitting up straight.

The findings are that the slumped-over position shuts the students down so that they cannot think clearly. The slumped-over position also can bring the students bad memories. While sitting up straight can help students do better on math exams.

Students who are not nervous about taking the math exam do not necessarily get help from better postures. But they do find that doing math while slumping over is more difficult.

These findings about body position can help people prepare for many different types of performance under stress, not just math tests. So when you feel stressed out, you can also try to sit up straight or stand tall. It can help you feel more positive and focus better.

Kite flying is a sport of sending kites up into the air by means of the wind, a light frame covered with paper, plastic or cloth.

People have been making and flying kites for about 2,000 years. But no one knows exactly when or how the first kite was made. In 478 BC, a Chinese philosopher, Mo Zi, spent three years making a wooden bird. Later, Lu Ban began to use bamboo to make kites. Another record of kite flying was in about 200 BC when the Chinese General Han Xin flew a kite with a flute tied to it. The flute made some sounds along with the Chu song as the kite rose into the air, which crashed the morale(士气) of the enemy quickly. The ancient Chinese also used bird kites—usually made of the traditional silk—to carry ropes（绳子） across rivers and valleys（山谷）.

In the 13th century, Marco Polo wrote about how the shipping businessmen flew the huge kite in the wind before the ship set sail. They predicted(预测) the voyage (航行) in this way. If the kite went high and straight, it meant a quick and successful voyage; but if it did not fly well, it was a bad omen(预兆).

Kites have also been used in scientific fields in the western world. In 1752, Benjamin Franklin tied a key to a kite and flew it in a storm to find out that lighting was a form of electricity. In the 1890s, Lawrence Hargrave invented the box kite to test ideas about flight. From 1898 to 1933, the National Weather Service used box kites to collect weather data. The Wright Brothers also experimented with kites. What they learned helped them make the first airplane in 1903.

Today, most people fly kites as a hobby. Kite festivals are organized in many cities in all parts of the world.