Dolores Huerta has worked hard most of her life to help other people. She has helped change things so that farm workers can have a better life.
      Dolores grew up in California. She was a good student and liked school. After she finished high school, she went to college and studied to be a teacher. After she became a teacher, Dolores noticed that many of her students were not getting enough food to eat. Some of them wore very old clothes. Dolores wondered how she could help them.
        Dolores decided to stop teaching so that she could spend more time helping the farm workers and their families. One thing she wanted to do was to get more pay for farm workers so they could buy their children the things they needed.
Dolores knew that many farm workers moved often from one place to another to help pick different kinds of fruits and vegetables. She began talking and writing about these workers. Even people who lived far from California read what Dolores wrote.
      Getting higher pay for the farm workers was not easy. Dolores worked hard to make sure that farm workers got good pay for their work. She knew that nothing would change unless people made new laws to help the workers. Through all her hard work, new laws were made that gave farm workers good pay.
     Dolores Huerta has worked for more than 30 years in many different ways to make life better for working people. She has shown how much one person can change things.

问题探究：

【1】新知学习

⑴梯形的中位线：连接梯形两腰中点的线段叫做梯形的中位线．

⑵梯形的中位线性质：梯形的中位线平行于两底，并且等于两底和的一半．

⑶形如分式 $\frac{m}{x+2m}$ （m为常数，且m＞0），若x＞0，则 $\frac{m}{x+2m}$ ，并且有下列结论：

当x 逐渐增大时，分母x+2m逐渐增大，分式 $\frac{m}{x+2m}$ 的值逐渐减少并趋于0，但仍大于0．当x 逐渐减少时，分母x+2m逐渐减少，分式 $\frac{m}{x+2m}$ 的值逐渐增大并趋于 $\frac{m}{2m}$ ，即趋于 $\frac{1}{2}$ ，但仍小于 $\frac{1}{2}$ ．

【2】问题解决

如图2，已知在梯形ABCD中，AD∥BC，AD＜BC，E、F分别是AB、CD的中点．