Energy is something that makes things work or causes changes. Light, heat, sound and electricity are forms of energy. Here is an introduction to them. 

When you talk about, or even think about Iron Man, the first image that pops into your head is the red and gold suit worn by Tony Stark. It provides Stark strength, protection against most attacks (攻击) and the power of flight. Iron Man is just a story, but the suit is not. Engineers call it an exoskeleton (外骨骼). It is the protective or supporting structure covering the outside of the body. 

In fact, the exoskeletons were used in hospitals at first. They have changed the lives of many people with injuries (受伤) or illnesses that affect movement. A disease had paralyzed Stacey Kozel and she could not walk anymore. But in 2016, she went hiking with an exoskeleton. In recent years, more and more exoskeletons have been used in factories. It is easy for people to do the tiring or dangerous work with the exoskeletons. "We usually pay attention to efficiency (效率). Using the exoskeletons saves us much time and money. The workers can make more products at the same time. "One factory manager said. "Also, wearing the exoskeletons can reduce the risk of injury. "What's more, exoskeletons can be used in rescue (救援) operations, providing workers with a lot of strength to lift heavy objects while protecting them from being hurt by falling weights.

However, the global spread of exoskeletons remains difficult. For one thing today's exoskeletons are expensive because they need to be charged (充电) regularly. For another, most exoskeletons can help people do only one type of movement. A company called SuitX is developing new forms of exoskeletons now. The company hopes people of all ages can use their products in the future.

That would be really cool, but some people worry that the technology will divide humanity. People who can afford exoskeletons will become stronger and achieve more than those without suits. We may end up with two classes of humanity: the superhumans and everybody else. That wouldn't be fair. Also, researchers have found that when people work in exoskeletons, muscles (肌肉) compete with each other, causing the brain to work less efficiently. Over time, it can also cause harm to the body.

So will exoskeletons harm or benefit humanity? No one knows for sure. More research is needed.

Everyone has their favorite food. Some might love chocolate. Some might love potato chips. Think about your favorite food. Have you ever wondered why your favorite food tastes so delicious？ The answer is about your tongue（舌头）and nose. There are some taste buds（味蕾） on your tongue. They give you the sense of taste. How do the taste buds work? In fact, there are many tiny hairs on the taste buds. These tiny hairs send messages to your brain about how something tastes. In this way, you know whether it is sweet, sour, bitter or salty. 

A person has about 10, 000 taste buds. They keep working all the time when we enjoy our food. The taste buds don't always stay the same. They are replaced（更新）every two weeks or so. 

However, as a person gets older, some of these taste buds don't get replaced. The old may only have 5, 000 working taste buds. That's why some foods may taste stronger for you than they do for the old. 

Besides your tongue, your nose also helps you learn about the taste of food. Sometimes, strong smells can even confuse（使 困惑）your sense of taste. Try holding an onion under your nose while eating an apple. What do you taste?

So next time you enjoy salty pizza and sweet ice cream, thank your tongue and your nose. Without them, you won't have any sense of taste at all. Without the sense of taste, life will be boring.