【推荐1】Bicycles are used by people of all ages around the world. It’s common in many cities to see thousands of bikes running down a street.

    1     It was thought that only men could run machines, and that women wouldn’t be able to control a bicycle. In the 1890s, though, with women’s growing independence(独立), bicycles offered women a way to travel by themselves.    2    

Most bikes today have two wheels, but you’ve probably seen other kinds, too.

Some people start riding bikes that have three wheels. The third wheel makes the bike easier to balance(平衡). These bikes are called tricycles. As you’ve seen, the bi- in bicycle means “two”.     3     Bikes with three wheels aren’t just for young children. They matter to adults because bikes with three wheels can help move people or things.

Some bikes also have only one wheel and no handlebars(把手).     4     The first part of the word, uni-, means “one”. Riding a bike with only one wheel is a balancing act—that’s why unicycles are used in the circus(马戏团).

    5     Bikes with four wheels are called quadracycles. Again, the first part of the word refers to the number of wheels. In this case, quadra- means “four”.

【推荐2】Have you seen The Wandering Earth? It’s a popular 3D movie, and you may have to wear 3D glasses to see it. The 3D glasses make the images (图像)from the movie look as if they were coming straight towards you.

More and more 3D movies are coming to theaters. Some say that 3D TV sets will come into our homes in the near future. 3D technology can make TV and movies are more exciting. However, people with eye problems may get headaches if they spend too much time watching 3D movies. Why?

When we look at an object, each eye sees it at a different angle. Our eyes send the two images to our brain, and the brain puts them together. 3D technology uses two film projectors (投影机). One projects a left-eye-image and the other projects a right-eye-image. 3D glasses allow us to see a different image in each eye. So, when we are watching a 3D movie, our brain can’t put together the images sent to our eyes. The brain needs to work harder at “reading” the images. That makes it easier for people with eye problems to get dizzy (头晕的) or have headaches. A famous eye doctor said if your eyes can’t focus on the same object at once, you will have trouble watching 3D movies.

【推荐3】What’s a spacewalk? Any time an astronaut gets out of a spacecraft(航天器) while in space, it is called a spacewalk. Astronauts go on spacewalks for many reasons. For example, experiments can be placed on the outside of a spacecraft. This lets scientists learn how being in space affects(影响) different things. By going on spacewalks, astronauts can also fix things instead of bringing them back to the earth to fix.

When astronauts go on spacewalks, they wear spacesuits to keep themselves safe. Inside spacesuits, astronauts have the oxygen(氧气) they need to breathe and the water they need to drink. To keep the astronauts and the spacecraft safe, the astronauts must leave and go back to the spacecraft through a special door. When on a spacewalk, astronauts use safety tethers to stay close to their spacecraft. Tethers are like ropes, connect the spacewalkers with the spacecraft. They keep astronauts from floating(漂浮) away into space. Another way astronauts stay safe during spacewalks is by wearing a SAFER. SAFER is worn like a backpack. It helps an astronaut move around in space.

How do astronauts train for spacewalks? One way is by going for a swim. Floating in space is a lot like floating in water. Astronauts practice spacewalks underwater in a huge special swimming pool. For every one hour they will spend on a spacewalk, astronauts need to train seven hours in the pool. Another way astronauts practice for a spacewalk is by using virtual reality(虚拟现实). It looks and feels just like a spacewalk.

Today, only three countries have finished spacewalks independently. They are Russia, the United States and China. The first person to go on a spacewalk in the world was Alexei Leonov from Russia. Zhai Zhigang is the first Chinese astronaut to go on a spacewalk. The world record of spacewalks is held by Russian astronaut Anatoly Solovyev. He has been on 16 spacewalks and spent more than 82 hours outside in space.