A、300 million. B、3 billion. C、Over 335 million. D、More than 28 million. C短文提到，PAI的研究显示，目前有超过3．35亿人口缺水，因此C正确。

A new study warns that about 30% of the world’s people may not have enough water by the year 2025. A private American organization called Population Action International did the new study.[23]It says more than 335 million people lack enough water now. These people live in 28 countries, mostly in Africa or the Middle East. PA1 researcher Robert Engelman says[23]by the year 2025, about 3 billion people may lack water. At least 18 more countries are expected to have severe water problems. The demand for water keeps increasing. Yet the amount of water on Earth stays the same. Mr. Engelman says the population in countries that lack water is growing faster than that in other parts of the world. The report says lack of water in the future may result in several problems. It may increase health problems. Lack of water may also result in more international conflict. Countries may have to compete for water in the future. Some countries now get 60% of their fresh water from other countries.[24]And the report says lack of water would affect the ability of developing countries to improve their economies. The PAI study gives several solutions to the water problem.[25]One way, it says, is to find ways to use water for more than one__purpose, Another way is to teach people to be careful not to waste water. A third way is to use less water of agriculture. The report also says longterm solutions to the water problem must include controls on population growth.
23. How many people are short of water now according to the PAI study?
24. What problems caused by water shortage are mentioned in the report?
25. What is one of the solutions to the water problem given by the study?