D

    Astronauts (宇航员) face many problems when living in space stations. One of them is food. People on Earth put together all the meals first and then send these meals to space stations by space shuttle. Because the food has to last a long time (sometimes up to three months), people have to store a lot of it in cans. The space station does not have a fridge, but it has a cool room to keep fruit and vegetables fresh. Astronauts also eat many other foods such as dried meat that do not need special care.

    Without the help of gravity sitting down to eat can be difficult. Astronauts sometimes have to fix themselves to the wall while eating. They also have to be very careful so that food does not float away.

阅读下列短文，从每题所给的四个选项（A、B、C和D）中选出最佳选项。

    Jogging is good for us and helps us live longer and healthier. It's easy to do and free. You do not have to spend money jogging. You can do it in a park or even in your home. But many people find it boring after jogging for a while. Then how can we keep jogging fun? Here are some ideas to make your jogging more interesting.

    First, you should choose to wear your favourite sports clothes and shoes when you jog. They make you more comfortable and more likely to run.

    Always jog outdoors. By changing your route, you can choose another street, and you will always have something interesting to enjoy when you jog.

Take along with your MP3 player and listen to your favourite songs when you jog. The music can make you excited and run farther without feeling bored.

    It's always more enjoyable with a friend. Make friends while jogging. Join a running club, find a new running partner, or invite an old friend to go jogging. It's better to find a friend who runs a little faster than you. Then you can try to catch up with him or her.

C

    If you go into the forest with your friends, stay with them. If you don't, you may get lost. If you get lost, this is what you should do. Sit down and stay where you are. Don't try to find your friends—let them find you. You can help them find you by staying in one place. There is another way to help your friends or other people to find you. You can shout or whistle (吹口哨) three times. Stop. Then shout or whistle three times again. Any signal (信号) given three times is a call for help.

    Keep up shouting or whistling. Always three times together. When people hear you, they will know that you are not just making a noise for fun. They will let you know that they have heard your signal. They will give you two shouts or two whistles. When a signal is given twice. it is an answer to a call for help.

    If you don't think that you will get help before night comes, try to make a little house with branches (树枝). Make yourself a bed with leaves and grass.

    When you need some water, you have to leave your little house to look for it. Don't just   walk away. Pick off small branches and drop (扔下) them when you walk to go back again easily. When you are lost, the most important thing to do is to stay in one place.

    Mica and her little sister got a tree house this year. "I'm Mica! I love my tree house!" This $28,000 tree house is a gift from their parents. Almost three metres above the ground, the platform (平台) was built between two large trees. "One of the things I really wanted was a little door within the big door. If you go up, you'll find that there is a door handle, which is of the kids' height. And there is an adult size door as well. I told the designer to make it feel like a secret hideout (躲藏处)," said Mica's mother Keenan.

    Bala Sundar and his wife came to America 20 years ago. Unlike Keenan and her husband, who bought a tree house for their daughters, the Sundars got one for themselves. "We wanted to have a regular place where we can relax. So we bought it," he said. With beds, tables and windows, it's a welcoming, comfortable space to spend a summer night.

    Both of these amazing tree houses were created by Dan Wright. He's the founder of Tree Top Builders Inc., and has built more than 400 tree houses since he started the company in 2003. "I think the sense of freedom and independence is why Americans can resonate (共鸣) with tree houses. They get people up off the ground and, for kids, their parents can't reach them anymore. They are up looking down, getting a new perspective on life," said Wright.

    North American black bears are shy animals. They are fearful by nature, and will usually run away if they see or hear people. Because of this, it can be difficult for scientists to learn about these animals.

    In order to study black bears, researchers from New Jersey, the US, catch bears and use drugs to help them go to sleep. Researchers then work out the size and the weight of the bears, take blood, to test for diseases, remove a tooth and take it to the lab to find out its age. From these studies, researchers want to find out how many bears live in New Jersey, how long they live, and how many babies they produce.

    But in Minnesota, the US, researchers study bears that are completely awake. The bears know the researchers' voices and they are not afraid of the research team. With the help of a few grapes to keep the bears busy, researchers can touch them to check their hearts, look at their teeth, and do other jobs. Researchers can also walk or sit with bears for hours and make videos to learn about their everyday lives."

    In both places, the main purpose is the same—to make sure there is a healthy population of black bears. But the research methods and the kinds of information that researchers are able to collect are quite different.