A scientist who developed a way to calculate how much water is used in the production of anything from a cup of coffee to a hamburger was awarded the 2008 Stockholm Water Prize. Professor John Anthony Allan of the University of London in Britain won the award for introducing the idea of "virtual water  ", a calculation method that has changed the nature of trade policy and research. Allan has written seven books and published more than 100 papers. The Stockholm International Water Institute said this idea is now embedded   in the production of foods and industrial products. The institute said Allan's work had made a big effect on global trade policy and research, especially in water-scarce   regions. "The improved understanding of trade and water management issues on local, regional and global scales are of the highest value for the successful and sustainable   use of water resources," it said. "People do not only use water when they drink it or take a shower," the institute said. "Behind the morning cup of coffee, there are 140 liters of water that was used to grow, produce, package and ship the beans." That is about as much water as a person in England uses on average for all daily drinking and household needs. "For a single hamburger, about 2,400 liters of water are needed. In the USA, the average person uses nearly 7,000 liters of virtual water every day." It said that was more than three times the average use of a Chinese person. Allan was awarded the prize because   _  .
he wrote seven books on trade policy he published more than 100 papers on water management he found a new kind of water in water-scarce areas he came up with the idea of virtual water
Question: A scientist who developed a way to calculate how much water is used in the production of anything from a cup of coffee to a hamburger was awarded the 2008 Stockholm Water Prize. Professor John Anthony Allan of the University of London in Britain won the award for introducing the idea of "virtual water  ", a calculation method that has changed the nature of trade policy and research. Allan has written seven books and published more than 100 papers. The Stockholm International Water Institute said this idea is now embedded   in the production of foods and industrial products. The institute said Allan's work had made a big effect on global trade policy and research, especially in water-scarce   regions. "The improved understanding of trade and water management issues on local, regional and global scales are of the highest value for the successful and sustainable   use of water resources," it said. "People do not only use water when they drink it or take a shower," the institute said. "Behind the morning cup of coffee, there are 140 liters of water that was used to grow, produce, package and ship the beans." That is about as much water as a person in England uses on average for all daily drinking and household needs. "For a single hamburger, about 2,400 liters of water are needed. In the USA, the average person uses nearly 7,000 liters of virtual water every day." It said that was more than three times the average use of a Chinese person. Allan was awarded the prize because   _  .
A. he wrote seven books on trade policy
B. he published more than 100 papers on water management
C. he found a new kind of water in water-scarce areas
D. he came up with the idea of virtual water
Answer: