问题
单项选择题
The concentration of a certain chemical in a full water tank depends on the depth of the water. At a depth that is x feet below the top of the tank, the concentration is 3
parts per million，where 0＜x＜4. To the nearest 0.1 foot, at what depth is the concentration equal to 6 parts per million
答案
参考答案：E
解析： “to the nearest”是中文中用四舍五入的方法取近似值的意思。
由题意可得：
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