如图，四边形OABC的四个顶点坐标分别为O（0，0），A（8，0），B（4，4），C（0，4），直线l：y=x+b保持与四边形OABC的边交于点M、N（M在折线AOC上，N在折线ABC上）．设四边形OABC在l右下方部分的面积为S₁，在l左上方部分的面积为S₂，记S为S₁、S₂的差（S≥0）．

小刘同学在探究“电流与电阻的关系”时，用到如下器材：电源电压6V、电流表、电压表各一只、定值电阻5Ω、10Ω、15Ω、20Ω、30Ω各一个，滑动变阻器标有“20Ω 1A”字样、开关一只．设计实验电路图如图所示，实验数据如表：

    Most American families are smaller than the families in other countries. Children in the USA will leave their parents when they grow up. They usually live far from their parents because they want to find good jobs. They often write to their parents or telephone them. And they often go to visit their parents on holidays.

    Parents usually let their children choose their own jobs. Americans think it is important(重要的) for them to make decisions(作决定).

    Children are also asked to do some housework at home. And in many families，children will get money from their parents for doing some housework. Because American parents want to let their children learn how to make money for their own use.

乙醇和乙酸是生活中常见的两种有机物．下列说法正确的是（　　）