In 1970, if 5 percent of the water use was for domestic purposes, approximately what was the daily average number of gallons of water used per capita for domestic purposes?

　　A.105

　　B.50

　　C.20

　　D.10

　　E.5

　　答案：A

　　If in 1900 the water use in Country K was the same as that in Country X, but increased at the constant rate of 3 billion gallons every year, then the two countries would again have had the same water use in approximately what year?

　　A.1910

　　B.1920

　　C.1930

　　D.1940

　　E.1950

　　答案：E