单选题 The United States is presently facing serious water problems. Rain and snow do not fall 1 across the country. The Northwest receives an abundance of rain, more than 80 inches each year in some areas. 2 , parts of the West and Southwest 3 less than ten inches per year. The Northeast and Midwest 4 have had sufficient supplies of water, but recently both regions have begun to experience water 5 . 6 one point, while New Yorkers were worrying about having enough water in which to bathe, farmers in Iowa prayed that their crops would 7 the hot summer months.
One area that has been hit especially 8 by the increasing shortage of water is the Southwest. Cacti flourish across its deserts, but crops cannot grow in the dry, sandy 9 10 there is extensive irrigation. In some areas, farmland is 11 to desert because the life-giving water has run out or become too 12 to pump from deep underground.
The Southwest receives its water from 13 two sources: large, underground reserves of water, called aquifers, and the 1, 400-mile-long Colorado River. The aquifers, which were formed over thousands of years ago, are being consumed slowly 14 surely. More water is taken out than nature can 15 . The aquifers receive only 8 percent of the total precipitation; the 16 92 percent either evaporates or flows 17 into the ocean.
The Ogallala Aquifer stretches 800 miles form western Texas to northen Nebraska. This underground 18 of fresh water, containing enough water to fill Lake Huron, is perhaps the largest in the world. 19 , its water level is 20 dropping. If water consumption continues at the present rate, the Ogallala may be dry in 40 more years.