3 . If you watch the sky for about an hour after the sun goes down, you may see some “moving stars”. But they’re not really stars. They’re man-made satellites. And the biggest of all is the International Space Station（ISS）. From May to July is the best season to watch the ISS flying over the earth. And people can see it with their eyes.

The ISS is the biggest satellite（人造卫星）and scientists want to live on it. They think that the best way to learn more about space is to live there.

When the space station is finished, it will be like a city in space. People will stay and study there with many of the things they have at home. Laboratories, living rooms and power stations are being built. The ISS is the most expensive space program. Billions of dollars are being spent on it every year.

Scientists hope that the ISS will be a stepping stone for future space exploration（探测）. “The ISS will help us understand the human body better, explore space and study the earth. It can help us make life on the earth better,” said Kathryn Clark, an ISS scientist.

Sixteen countries are part of the program: the US, Russia, Canada, Japan, Brazil and 11 European countries. China isn’t an ISS country, but it has helped with some of the experiments. In 2003, China sent some rice up to the ISS to find out what space would do to it.

4 . How much do you know about the solar system?The following passage will tell you.

The earth is a planet.It as well as seven _____ planets goes around the sun.We _____ the eight planets and the sun the solar system.The first planet,_____ the sun,is Mercury(水星).It is 58 million _____ from the sun.Venus(金星)is the second planet next to the sun,and _____ planet,the earth,is the third.It is 150 million kilometres from the sun.

Jupiter(木星),Saturn(土星),Neptune(海王星)and Uranus(天王星)are all _____ than the earth,_____ Venus,Mars and Mercury are smaller than the earth.

Animals,trees and humans can only _____ on the earth—the other planets in our solar system do not _____ air or water.Do any planets in other galaxies have ______?We don't know about it.