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问题 选择题

二次方程ax2+bx+c=0的两根为-2、3，a＜0，那么ax2+bx+c>0的解集为 [ ]

A.{x|x>3或x＜-2}

B.{x|x>2或x＜-3}

C.{x|-2＜x＜3}

D.{x|-3＜x＜2}

答案

答案：C

填空题

如果（2x+3）（ax-5）=2x2-bx+c，则a=（    ），b=（    ），c=（    ）。
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单项选择题

C


Americans use more water than any other people in the world. If we continue to use water at the rate we do now, we will soon not have enough to meet our needs. In 1980, 40 billion gallons were used each day in the United States. In 1990, 700 billion gallons were used. The average Americans use almost 90 gallons of water a day for personal use. And much move water is needed to make the things American people like to have. For example, it takes thousands of gallons of water to make one pound of beef for the dinner table. It takes more than 100000 gallons of water to make a car. If we include these uses of water, the average American uses about 2000 gallons of water a day．

Americans used ______ gallons of water each day for personal use in 1990．

A．40 billion

B．90

C．700 billion

D．2000
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