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

The ISS is the biggest satellite 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 spent on it every year.

Scientists hope that the ISS will be（B）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 Cark, 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 county, but it has helped to do some experiments. In 2003, China sent some rice up to the ISS to find out what space would do to it.

Scientists want to live on the International Space Station because they think it is _______ to learn about space. People _______ billions of dollars every year on it. There are _______ member countries in ISS. China is not one of them but China sent some rice up to the ISS to help with _______.