题目

While only about 200 astronauts have had the excitement of looking down at Earth and commanding systems on the International Space Station, actually thousands of everyday middle-school students have experienced  by Middle School Students, or EarthKAM, a camera system.EarthKAM is an educational activity and outreach(扩展)investigation that also results in temote Earth sensing and observation. Using the Internet, the students control a special digital camera fixed aboard the space station, enabling them to photograph the Earth's cosastlitnes, mountain ranges and other geographic items of inte飞机每小时飞行500米。（______）