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 uses 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 100,000 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 in 1980.

A．40 billion

B．90 billion

C．700 billion

D．200 billion

如果使用矩形选择工具无法绘制出比例与大小任意的矩形，其原因可能是下列哪几项（）。

A.此工具的“样式”被定义为“约束长宽比”

B.此工具的“样式”被定义为“固定大小”

C.定义了一个较大的羽化值

D.“消除锯齿”选项被选中了