Its a strange partnership, but a very effective one: Satellites and space-shuttle-carried radar are helping archeologists. How? By seeing through sand or through treetops to locate important archeological sites.　　Take, for example, the second 1981 flight of the Space Shuttle Challenger. During that mission, a powerful, experimental radar was pointed at a lifeless stretch of desert in Egypt called the Selima Sand Sheet . To everyones surprise, the radar penetrated through the sand to the harder rock beneath. On the surface, there is a little indication that Africas Sahara Desert was never anything but a desert. When the archeologists studied the radar images, they saw what seemed to be impossible: there was sand-buried landscape that was shaped by flowing water; traces of ancient riverbeds appeared to be over nine miles wide, far wider than most sections of the present-day Nile River. Today, the area is one of the hottest, driest desert in the world.　　More recently, Landsat 4, a special Earth-mapping satellite, aided in the discovery of ancient Mayan ruins in Mexico. Landsat can, with the help of false-color imagery, see through much of the area. Armed with these maps, a five-person expedition took to the air in a helicopter.　　41 With the help of the space-shuttle-carried radar, archeologists found　　B traces of ancient riverbeds under the Sahara Desert.　　D a mountain beneath the Sahara Desert.　　A It was an old avenue,　　C It was shaped by flowing water.　　43 The stream-rounded pebbles and Stone-Age axes which were found along the ancient river banks show that　　B ancient people didnt know how to make weapons.　　D early humans were good at fighting with sharp weapons.　　A old New England fences.　　C the expedition members.　　45 Which of the following best summarizes the main information of the passage?　　B Without high-tech, the archeologists work would come to a stop　　D High-tech makes the archeologists work more fruitful.

　　Its a strange partnership, but a very effective one: Satellites and space-shuttle-carried radar are helping archeologists. How? By seeing through sand or through treetops to locate important archeological sites.　　Take, for example, the second 1981 flight of the Space Shuttle Challenger. During that mission, a powerful, experimental radar was pointed at a lifeless stretch of desert in Egypt called the Selima Sand Sheet . To everyones surprise, the radar penetrated through the sand to the harder rock beneath. On the surface, there is a little indication that Africas Sahara Desert was never anything but a desert. When the archeologists studied the radar images, they saw what seemed to be impossible: there was sand-buried landscape that was shaped by flowing water; traces of ancient riverbeds appeared to be over nine miles wide, far wider than most sections of the present-day Nile River. Today, the area is one of the hottest, driest desert in the world.　　More recently, Landsat 4, a special Earth-mapping satellite, aided in the discovery of ancient Mayan ruins in Mexico. Landsat can, with the help of false-color imagery, see through much of the area. Armed with these maps, a five-person expedition took to the air in a helicopter.　　41 With the help of the space-shuttle-carried radar, archeologists found　　B traces of ancient riverbeds under the Sahara Desert.　　D a mountain beneath the Sahara Desert.　　A It was an old avenue,　　C It was shaped by flowing water.　　43 The stream-rounded pebbles and Stone-Age axes which were found along the ancient river banks show that　　B ancient people didnt know how to make weapons.　　D early humans were good at fighting with sharp weapons.　　A old New England fences.　　C the expedition members.　　45 Which of the following best summarizes the main information of the passage?　　B Without high-tech, the archeologists work would come to a stop　　D High-tech makes the archeologists work more fruitful.