13．小明有一圆锥形水杯，里面装满了水，小明喝了几口，发现水面下降了$\frac{1}{3}$，那么剩下的水是原来的（ ）
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| A． | $\frac{2}{3}$ | B． | $\frac{4}{9}$ | C． | $\frac{8}{27}$ | D． | $\frac{1}{2}$ |
为民小学六年级有250名同学，参加课外兴趣小组分布情况如图．