《托福阅读理解试题节选.docx》由会员分享，可在线阅读，更多相关《托福阅读理解试题节选.docx（3页珍藏版）》请在taowenge.com淘文阁网|工程机械CAD图纸|机械工程制图|CAD装配图下载|SolidWorks_CaTia_CAD_UG_PROE_设计图分享下载上搜索。
1、 托福阅读理解试题节选 Groundwater is the word Groundwater is the word used to describe water that saturates the ground, filling all the Groundwater is the word used to describe water that saturates the ground, filling all the available spaces. By far the most abundant type of groundwater is meteoric water; th
2、is is the groundwater that circulates as part of the water cycle. Ordinary meteoric water is water that has soaked into the ground from the surface, from precipitation (rain and snow) and from lakes and streams. There it remains, sometimes for long periods, before emerging at the surface again.At fi
3、rst thought it seems incredible that there can be enough space in the “solid” ground underfoot to hold all this water. The necessary space is there, however, in many forms. The commonest spaces are those among the particlessand grains and tiny pebblesof loose, unconsolidated sand and gravel. Beds of
4、 this material, out of sight beneath the soil, are common. They are found wherever fast rivers carrying loads of coarse sediment once flowed. For example, as the great ice sheets that covered North America during the last ice age steadily melted away, huge volumes of water flowed from them. The wate
5、r was always laden with pebbles, gravel, and sand, known as glacial outwash, that was deposited as the flow slowed down. The same thing happens to this day, though on a smaller scale, wherever a sediment-laden river or stream emerges from a mountain valley onto relatively flat land, dropping its loa
6、d as the current slows: the water usually spreads out fanwise, depositing the sediment in the form of a smooth, fan-shaped slope. Sediments are also dropped where a river slows on entering a lake or the sea, the deposited sediments are on a lake floor or the seafloor at first, but will be located in
7、land at some future date, when the sea level falls or the land rises; such beds are sometimes thousands of meters thick. In lowland country almost any spot on the ground may overlie what was once the bed of a river that has since become buried by soil; if they are now below the waters upper surface (the water table), the gravels and sands of the former riverbed, and its sandbars, will be saturated with groundwater. So much for unconsolidated sediments. Consolidated