【推荐2】It often takes astronauts days to go to the moon. But will people live there? Will people build _______ city on the moon?

Some people think it is ________. But it won’t be easy. There isn’t ________ oxygen (氧气) on the moon. Spaceships (宇宙飞船) will need to bring oxygen from the earth. Food will be a problem, too. How will people grow vegetables? There isn’t any water, ________ scientists think that they might find some ice. The energy (能量) for the city won’t be a problem—it will come ________ the sun.

________ will go to the moon? Maybe scientists will go there. The moon is an interesting place for ________. It is never cloudy or rainy on the moon, so it is a good place ________ the stars and planets. Maybe we will build a university for them. We will probably build a hotel for ________, too. There are no beaches on the moon, but people can walk on the moon and take photos of the earth.

Will it ________ ? Maybe. But one thing is true: A visit to the moon hotel will be very expensive!

【推荐3】Maybe you know a lot about the city you live in. You may even know some interesting facts about earth, but ________ do you know about Mars? Will there be ________ there just like people on Mars?

Mars is the fourth planet from the sun and it’s the most like earth, but it’s much ________ than earth because it’s farther from the sun. It’s also the only planet whose surface can be ________ from earth.

Mars is often called “the red planet” because the rocks on it have a dark ________ color. There are strong winds on Mars that can ________ dust into the hills. For many years, people have ________ Mars. They have sent instruments and robots there. Some of the robots got there, ________ most failed. NASA(美国国家宇航局) sent two robots to Mars two years ago. They wanted to ________ signs of water and life on Mars. Some day, humans will travel to Mars and have an even ________ look at our red neighbor. Maybe it could be you!