Now machines are widely(广泛地)used all over the world. Why are machines so important and necessary for us? Because they can help us to do things better and faster.

A washing machine helps us to wash clothes fast. A printing machine helps us to print a lot of books, newspapers, magazines and many other things fast. Bikes, cars, trains and planes are all machines. They help us to travel faster than on foot.

The computer is a wonderful machine. It was invented(发明) not long ago. It not only stores(贮存) information but also stores numbers millions of times as fast as a scientist does.

Let’s study hard and try to use all kinds of machines to build China into a modern country.

  The idea that red means stop and green means go has influenced our lives in more ways than just traffic signals(信号). We have been taught from a young age that the color red means danger and green means it's okay to move forward. But why were those colors chosen for traffic lights in the first place? For something we have to look at every day, why couldn't they have been prettier colors?

    Well, it's important to know that before traffic lights for cars, there were traffic signals for trains. At first, railway companies used red to mean stop, white to mean go, and green to mean warn. As you could imagine, trains ran into a few problems with white meaning go. For example, one train mistook a bright star for a white light and something unexpected happened. Because of that, railway companies finally moved green meaning go and used yellow to mean warn. And it's been that way ever since.

    Red has always been a color that means danger, long before cars were even around. This most likely started because it's the color with the longest wavelength (波长) so it can be seen somewhere farther than other colors.

    But, believe it or not, yellow was once used to mean stop. Back in the 1900s, some stop signs were yellow because it was too hard to see a red sign in a poorly lit area. Finally, highly reflective materials(高反射材料) were developed and red stop signs were born. Since yellow can be seen well at all times of the day, school zones, some traffic signs, and school buses continue to be printed yellow.

    So next time you are impatiently waiting at a traffic light, don't get so mad at them, they've certainly come a long way.

Lockheed Martin, American space system company (空间系统公司) has found a really cool way to inspire the young minds of today to the research fields in Science, Technology, Engineering and Math (STEM).

It may look like a normal yellow bus, but all the magic happens once you get inside. Meet the“Mars (火星) Experience Bus,” part of Lockheed Martin’s new“Generation Beyond” national education program to get the kids joining in studying what goes on outside of our home planet. The bus offers a virtual reality (VR,虚拟现实) experience making the teenagers feel like they are driving on Mars.

The VR experience was developed by taking advantage of software (软件) created for today’s best video games, so you can imagine the picture shown is top level. The kids do seem really excited to see the bus take a virtual trip on the red planet and search unknown places. It’s certainly a great way of leaning about the universe by virtual reality working on a common bus.

The Lockheed Martin’s bus will start a tour in the United States to allow kids from different parts of the country to take a ride in it. The Generation Beyond project also includes an iPhone app for iOS providing real-time information about weather reports for Mars, and there’s also a free deep space course for middle school teachers and students.

The traditional Chinese lunar calendar divides the year into 24 solar terms. Grain Rain (谷雨), as the last term in spring, starts on April 19 and ends on May 4.

Grain Rain comes from the old saying,“Rain brings up the growth of hundreds of grains”, which shows that this period of rainfall is very important for the growth of crops. Here’s something that you may not know about the Grain Rain.

（1）. ________

Grain Rain falls between the end of spring and the beginning of summer, and the temperature rises much higher than it does in March. With dry soil and heavy winds, sandstorms may happen more often. （2）. ________

There is an old custom in southern China that people drink tea on the day of Grain Rain. Spring tea during Grain Rain is good for the eyes. It is also said that drinking tea on this day would prevent bad luck.

（3）. ________

People in northern China have the tradition to eat the vegetable toona sinensis during Grain Rain. An old Chinese saying goes“toona sinensis before the rain is as tender as silk (嫩如丝)”. The vegetable is good for the stomach and skin.（4）. ________

The Grain Rain Festival is celebrated by fishing villages in northern China. Grain Rain marks the start of the fishermen’s first voyage (航行) of the year. The custom dates back to more than 2000 years ago.

  a. Eating toona sinensis

  b. Sandstorms happen

  c. Grain Rain Festival

  d. Drinking tea