阅读理解 In recent years, remote-sensing technologies have become ordinary in archaeological fieldwork (实 地考察). Such tools for excavation produce rapid results and cause no damage to archaeological sites. They are highly accurate and usually cost effective. Here are three of the modern archeologist's most trusted remote-sensing tools. As the simplest of the remote-sensing techniques that archeologists use, aerial (空中的) photography allows experts to see aspects of a site that may be invisible from the ground, such as the way in which something such as a town, garden, or building is arranged and traces of old walls and roads. The technique involves taking photographs with conventional cameras and filming from airplanes, helicopters, hot-air balloons, or other airborne vehicles. Geographic Information System (GIS) contains a large amount of field data archeologists typically collect in and around excavation sites. While in the field, archeologists use GIS on their computers to make and manage detailed site maps, and they can combine the results of remote-sensing tests with maps of the region created with the aid of Global Positioning System. Resulting maps sort the most archeologically promising areas and display these sites three-dimensionally. Ranging in size from small handheld models that one places against the ground to larger ones that one drags across a site, Ground Penetrating Radar (GPR) devices use low-power radio waves to detect changes underground. Unlike traditional radar, which broadcasts into the air and uses a dish to focus the returned waves, GPR uses a small but sensitive receiver placed directly against the ground. Depending on their needs, archeologists can adjust radio frequencies upward for shallow sites or downward for deeper areas, though GPR devices produce the greatest definition (清晰度) when reading depths of three feet or less. 1. We can learn from the text that the remote-sensing tools . A. will replace traditional archeological tools B. are more difficult to use than traditional tools C. have been widely and efficiently used in archeology D. help archaeologists discover more archaeological sites 2. Aerial photography is helpful . A. in seeing what can't be seen on the ground B. in analyzing how old an archaeological site is C. in reflecting the changes of an archaeological site D. in taking large-sized photos of an archaeological site 3. Ground Penetrating Radar (GPR) devices are different from traditional radar in that . A. their sizes are completely different B. traditional radar uses low-power radio waves C. the length of waves they send out is different D. GPR devices can detect changes underground 4. Archeologists can get a detailed site map by . A. aerial photography B. Geographic Information System C. Global Positioning System D. Ground Penetrating Radar