题目

    The expression“a thirst for knowledge may soon have a new meaning for millions of people who have no way to get clean water. Researchers have developed a book with specially treated pages that can turn dirty water into clean and drinkable water. They say their invention could improve the lives of many in the developing world.     About 700 million people around the world are at risk of disease or even death because their drinking water is not clean. The water is polluted by harmful bacteria.     The book contains 25 pages. Each page is about one millimeter thick. The pa ________，不是清泉，是天上虹________，沉淀着彩虹似的梦。