Every year on April 22, People all over the world celebrate Earth Day. It is a time to work to keep our earth clean. People plan projects to clean up the land, air and water.
    U.S. Senator Gaylord Nelson first thought of the idea for Earth Day in 1962 when he saw polluted rivers and cities with smoke. He needed to get support from Americans to clean up the earth. Finally, on April 22, 1970, 20 million Americans celebrated the first Earth Day! Now many countries around the world celebrate it, and you can, too.
How can you celebrate Earth Day? Here are a few ideas:
Join a clean-up project------Clean up your street or a favorite beach.
Save energy------Turn off the lights when you leave a room, and use public transportation.
Use less water.
Reduce(减少)/ Reuse/ Recycle ------ Practice the three Rs: First, reduce how much you use. Then reuse or recycle what you can.
You can make a difference on Earth Day and every day!

如图，已知 $\angle 1=\angle 2,\angle 3=\angle 4,\angle E={90}^{\circ }$ ，试问：AB∥CD吗？为什么？

解：∵ $\angle 1+\angle 3+\angle E={180}^{\circ }$ （____）

$\angle E={90}^{\circ }$ （____）

∴∠1+∠3=____（____）

∵ $\angle 1=\angle 2,\angle 3=\angle 4$ （____）

∴∠1+∠2+∠3+∠4=180°

∴ AB∥CD（____）

若实数$x,y$满足$\{\begin{array}{c}x+y\ge 3\\ 2x-y\le 0\\ x\ge 0\end{array}$，则$z=y-x$的最小值为   （   ）

过去，国外品牌汽车在中国市场销售，必须通过品牌汽车厂商授权的专卖店进行。2015年1月，中国实行“平行进口车”制度，允许贸易商直接在国外购买汽车，进口到国内销售。中国推行“平行进口车”制度意在(     )

学以致用，探究问题

在探索社会主义建设道路上，我国经历了曲折与坎坷。

请回答：