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　　托福阅读插入题例题

　　4. 跨段式：

　　(1)跨段非过渡

　　①　These+n

　　例题18：

　　Regularly flowing rivers and streams that originate within arid lands are known as "endogenous." These are generally fed by groundwater springs, and many issue from limestone massifs, such as the Atlas Mountains in Morocco. Basaltic rocks also support springs, notably at the Jabal Al-Arab on the Jordan-Syria border. █Endogenous Rivers often do not reach the sea but drain into inland basins, where the water evaporates or is lost in the ground. █Most desert streambeds are normally dry, but they occasionally receive large flows of water and sediment.█

　　Deserts contain large amounts of groundwater when compared to the amounts they hold in surface stores such as lakes and rivers. █But only a small fraction of groundwater enters the hydrological cycle-feeding the flows of streams, maintaining lake levels, and being recharged (or refilled) through surface flows and rainwater. In recent years, groundwater has become an increasingly important source of freshwater for desert dwellers. The United Nations Environment Program me and the World Bank have funded attempts to survey the groundwater resources of arid lands and to develop appropriate extraction techniques. Such programs are much needed because in many arid lands there is only a vague idea of the extent of groundwater resources. It is known, however, that the distribution of groundwater is uneven, and that much of it lies at great depths.

　　Look at the four squares [█] that indicate where the following sentence could be added to the passage

　　These sudden floods provide important water supplies but can also be highly destructive.

　　Where would the sentence best fit?