单项选择题

The amount of usable water has always been of great interest in the world. 66 springs and streams sometimes means control, particularly in the 67 areas like the desert. The control is possible even without possession of large areas of 68 land. In the early days of the American West, gun fights were not 69 for the water resources, and laws had to be 70 to protect the water rights of the 71 and the use of the water resources accordingly. 72 is known to us all, there is not 73 water in all places for everyone to use as much as he likes. Deciding on the 74 of water that will be used in any particular period 75 careful planning, so that people can manage and use water more 76 . Farmers have to change their use of or demand for water 77 the water supply forecast. The 78 water supply forecast is based on the water from the 79 than from the below. Interest is 80 in the ways to increase rainfall by man-made methods, and to get water from the winter snow on mountain 81 With special equipment, some scientists are studying the ways in which the mountain snow can be 82 , and with the help of a repeater station, they send the 83_. data to the base station. The operator at the base station can get the data at any time by 84 a button. In the near future, the forecast and use of water probably depend on the advance knowledge of snow on mountains, not of water underground.