There are many kinds of 1. transportation now. Which one do you like best, by train, by bus or by plane? Now let's look at these three kinds of transportation. 2.The fastest way to travel is by plane. If you want to save time, 3.乘火车是最好的选择. A plane ticket can also be easier to book, and there are 4.(hundred) of planes leaving half an hour to everywhere. But it is much 5.(expensive) than traveling by train or by car. Many people prefer to traveling together by train. Because the train is cheaper than the plane and you can see the beautiful scenery out of the windows. But sometimes people are very noisy on the train. And it's very small and crowded inside the train. Taking a car is great. You can feel freer in your own car and you can move quickly from place to place at any time you like. 6.But sometimes you may be late because of the heavy traffic  .You have to pay for a car park and petrol . Cars are less comfortable than trains. You can't sleep or relax when you drive. Cars pollute the air more than trains, too.

    There is a lot of salt on the Earth, and it mixes very well with water.

There is some salt in all water. Water on the land runs into lakes and rivers. These rivers run into the seas and oceans. They carry a little salt with them. Some of the ocean water moves into the air and clouds. It evaporates. Salt cannot evaporate. It stays in the oceans.

    The water in the oceans has more salt than river water. There is about 3. 5% salt in the ocean water. Some seas have more salt than others.

    Some of the water leaves the lakes. It evaporates, but the salt cannot. These lakes are very salty. There are two famous lakes like this. They are the Dead Sea in the Middle East and the Great Salt Lake in Utah(犹他州）in the United States. They are much saltier than the Atlantic Ocean（大西洋）and the Pacific Ocean(太平洋）.

    People in Western countries are eating less meat these days, whether for their health or because they want to protect animals. But now they have another reason.

    Eating less meat can help to prevent climate change, according to a recent study published in Nature.

    Raising livestock (家畜) is bad for the environment. When animals like cows digest (消化) food, their stomachs make greenhouse gases, which are a major cause of global warming. Seventeen percent of greenhouse gas emissions (排放) come from livestock farming, The New York Times reported.

    In addition, to raise these livestock, people have to cut down forests and turn them into farms. Forests play a key role in fighting global warming because they absorb greenhouse gases.

    Eating less meat according to certain guidelines could cut global food-related emissions by nearly a third by 2050, the study found. Maintaining (保持) a vegetarian diet in the long term could bring down emissions by 63 percent.

    But eating less meat won't be easy. According to the study, people in Western countries will need to eat 90 percent less meat than they do now in order to have an impact (影响) on our climate. Scientists are now trying to find new foods to replace meat.

    Some say that insects (昆虫) could help. A 2013 UN report said that eating insects is healthier and better for the environment. They produce 75 percent less greenhouse gases than livestock.

    Some experts are creating lab-grown meat. They make meat in a lab using livestock cells (细胞). In March, US company JUST said people in the US might be able to buy its lab-grown meat by the end of this year.

    As space science develops, man has learned more and more about space. Space is not only amazing but also dangerous. While working in space, spacemen are facing danger as well as success.

    Scientists have found out that radiation(辐射) is the greatest danger to spacemen in space. When spacemen are working in space, they are in danger of radiation from the sun and other stars, which is bad for their health. The damage(危害) done by radiation won't be discovered until their children or even grandchildren are born. Some special medicine may work a little, but no really helpful medicine has been.

    Space junk is also thought a great danger to spacemen. It's reported that there are 9, 000man﹣made things flying in space. About 30% of these are satellites, 10% are spaceships, and the rest are space junk. An explosion(爆炸) in 1996made a cloud of 300, 000 fragments, each at least 4mm in size, and even a small piece of these knocked against a spaceship window and did some damage. Scientists are watching and reporting any possible danger all the time. They are working on helpful ways to do with space junk.

    Although space is really dangerous, it interests everyone on the earth. In the near future, it may become usual for people to spend a few days in a space hotel. We may even choose to leave the earth and live in space in a few years. So we should care for space and do something to help improve the space environment.