In his new book "Water: the Epic Struggle for Wealth, Power and Civilization", Solomon tells a story of  transformative inventions like the waterwheel, irrigation, the steam engine and hydro-electric power. Solomon says some of these innovations are actually _________________________________.

 "There are now 45,000 such multipurpose dams around the world, half of them, by the way, in China. _________________________________, because the Green Revolution was not just a matter of hybridization of cropping and fertilization, but needed massive amounts of water." 

Water use grew twice as fast as world population in the 20th century, Solomon says, but today our ability to exploit water can no longer match the demand. "We simply don't have enough water to do the economic things that we need to do with it or want to do with it for 6,500,000,000, much less than 9,000,000,000 that we are becoming." 

According to the United Nations, 1,000,000,000 people around the world lack access to safe drinking water and 2,500,000,000 people lack adequate sanitation. _________________________________. Solomon says he saw this inequity clearly during his 2004 visit to a rural village in southeastern Kenya, where he'd gone as a volunteer to help build a simple mud dam.

答案：

(1)at the root of today's worsening water scarcity problems
(2)But they were one of the great facilitators of the Green Revolution
(3)Poorer nations are the hardest hit, with enormous gap between the haves and have-nots