But the flesh and the bones make up the largest part of the body, and there is a good deal to be learned about them. You know the general appearance of both flesh and bone from the parts of animals which you see in the butcher’s shop.

Bone is hard, and of a white color; indeed, it looks more like a piece of wood or stone than a part of a living animal. But bone is a real part of the living body, and it grows and is nourished (滋养) just as the body is. If a man breaks the bone of his arm or his leg, it is firmly bound up, to prevent the broken parts from moving out of the proper places, and in time then bone grows together again and becomes quite strong.

The bones are fastened together by various kinds of joints(关节). They form the framework of the body, and give it strength to retain its proper shape. This framework is called the skeleton(骨架). Some animals, such as worms and slugs, have no skeleton; and others, such as shellfish, have a kind of hard covering or skeleton outside.

The most important part of the skeleton is the backbone. It is so important that naturalists divide all animals into two classes,—those which have a backbone and those which have none. All the higher animals, including man, have a backbone, or vertebral column as it is called. They are therefore called vertebrate(脊椎的) animals. The others are called invertebrate animals.

Humans' Greatest Achievements

The Earth is 4.5 billion years old, but the human race has lived on it for just 200,000 years, In that short time, we have achieved some amazing things.

【小题1】 The list is almost endless. The invention of the airplane has changed our lives. The discovery of antibiotics(抗生素) has saved the lives of millions of people. Can you imagine living without electricity? What about the printing press(印刷术)? Without the printing press, you wouldn't be reading this. In the last 50 years, there have been great achievements in communication, such as radio, TV, computers, the Internet, and smart phones. 【小题2】

What about the arts? The arts have brought pleasure to many people, but are the Beatles and Bach more important than antibiotics? 【小题3】

Finally, we must not forget humans' early achievements. 【小题4】 We can't imagine modern life without cooked food and cars.

What are humans' greatest achievements? To answer the question, we need to decide what we mean by "great".【小题5】. Or is it just something that makes us say "Wow," like the Great Wall? What do you think?

A myth is something that is not correct, but many people believe it. There are a lot of myths about the human brain.

One of the biggest myths is that we only use 10% of our brains. The next part of the myth is that if we can learn to use the rest of our brains, then we’ll be much smarter. People say this all the time, but it’s completely not true! The truth is that although we don’t know everything about the human brain, we know that each part of it has an important function. Modern scientists think the “10% myth” silly.

Another popular myth is about being “right brained” or “left brained”. According to this myth, people who use the right side of their brains are more artistic and creative. People who use the left side of their brains are better at math and science. This is as popular as the 10% myth, and it’s also wrong. In 2013, a study at an American university tested the right brain and left brain myth. The study shows we use the left brain as much as the right brain.

It’s true that we use different parts of our brains for different things. We use our left side for language more, and our right side when we need to pay attention. But there is no evidence that creative people use the right side more or that scientific people use the left side more.

We’ve talked about myths, so let’s look at a few interesting facts about the brain. First of all, the brain feels no pain. Second, about 75% of the brain is made up of water. It’s also the fattest organ in your body. Here’s another interesting fact about the brain. Around the time you turn 18 years old, it stops growing.