A tornado (龙卷风) is a kind of strong storm with air which moves in a circle quickly. They can move over 200 miles per hour and cause a lot of damage (损坏). As they move across the land, they can easily pick up cars, trucks, and even houses, and then throw them very far. It is important to find a safe place if a tornado gets close.

A safe place could be a basement ( 地下室) or the lowest floor. If you are in a home without a basement, try to find a first-floor bathroom or a small room without windows in the middle of your house. You should curl up (蜷缩) into a ball and cover your head and neck with your hands.

But there are some people who actually want to get close to tornadoes. They are scientists who want to learn more about tornadoes. One of the best ways to do this is to get as close as possible to the tornado. They use special tools to measure (测量) what is happening in and around a tornado.

One special tool is called a tornado probe ( 探测仪). Inside the tornado probe, there are sensors (传感器) to measure wind speed, temperature, pressure, and direction.

Some probes even have cameras, so the scientists can see and understand what it's like to be in a tornado.

To be able to get these measurements, the scientists have to get a tornado probe near or into a tornado. Scientists will try to guess where a tornado will go next. Then they drive to that location and put down the probe. If they do not guess correctly, they pick up their probe and try another place. If they are right, the tornado will go near or even right over the probe. Then they take all of the measurements

from the probe and use them to predict where future tornadoes may form (形成) and travel. And they can give people some warning to keep away from a dangerous tornado.

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Do you know{#blank#}9{#/blank#} (this) two boys? Oh, they are {#blank#}10{#/blank#} (I) cousins, Bob and David. I love my family very much

Today，young people spend about six hours a day in front of a TV or a computer and less than four minutes playing outdoors.It is not healthy for the mind and the body when time spent using technology replaces outdoor time.

Some health experts call green time "vitamin G".Kids who don't get outdoors much are likely to have trouble in school.Doctors believe that is because being outdoors excites the mind more than sitting around indoors.Even those who usually spend a lot of time outdoors notice a difference when they don't get green time.Madelyne P，14，says ， "I feel more tired when I don't get outdoors."

Researchers believe the positive effects of green time come from the physical activity in pastimes such as hiking or boating.Exercise produces brain chemicals that improve learning，mood，and sleep.It also improves learning by increasing connections between nerve cells that are important in learning and memory.Some schools hold classes outside for those reasons.Student Hannah Smith，says she believes the outdoors helps her focus and gets her to learn.Learning in a forest sparked her interest in art and photography，too.

Even doctors are helping give their patients a dose of（一剂）vitamin G.Miller writes "park prescriptions （处方）"for her patients because，being outdoors is good for health.She finds that when she gives patients park prescriptions，they are likely to continue with them.

Getting outdoors can be simple，just like calling together your family for a picnic lunch.All it takes is five minutes or more of green time.

Get outside，and get your vitamin G!

难度系数：★★

Every school day, we use schoolbags to carry all of our things to school. They are a big part of our lives. But have you ever thought about the history of the schoolbag?'. 

In the Han Dynasty（汉朝）, students in old - style private schools used bamboo boxes to carry books to school. People consider the bamboo boxes to be the earliest schoolbags. There were usually two or three layers（层）in the box. Kids put different things like books, brushes, ink stones（砚）and paper in the boxes. 

Hundreds of years later, people developed a new kind of schoolbag called the budai, or the " hip - pocket ". The budai was lighter than the bamboo box. With the founding (成立) of the People's Republic of China, military rucksacks（军用背包 )became popular. Many people carried them when they were in school. Ask your grandparents or parents about these bags. Maybe they can tell you about their experiences of carrying them when they were in school. 

A new style of schoolbags has appeared in recent years. Many of them have colorful and fashionable designs（时尚的设计） on them, such as pictures of cartoons or pop stars. And they are more comfortable to use. Some students pull wheeled bags filled with heavy textbooks and others carry backpacks. 

Schoolbags are still changing. Can you imagine what future schoolbags will be like?