索取____          幸福____

慈爱____          经常____

如图甲所示，两根足够长的平行光滑金属导轨MN、PQ被固定在水平面上，导轨间距L=0.6m，两导轨的左端用导线连接电阻R₁及理想电压表，电阻r=2Ω的金属棒垂直于导轨静止在AB处；右端用导线连接电阻R₂，已知R₁=2Ω，R₂=1Ω，导轨及导线电阻均不计．在矩形区域CDEF内有竖直向上的磁场，CE=0.2m，磁感应强度随时间的变化如图乙所示．在t=0时刻开始，对金属棒施加一水平向右的恒力F，从金属棒开始运动直到离开磁场区域的整个过程中电压表的示数保持不变．求：

      What does it mean to be green? "Green" is more than just a color. It also means taking special steps to protect the environment. Why green? Plants are green, and without them, the earth wouldn't be such a lovely home for us.

     Every day, people make a lot of trash and pollution. What can you do? Here's a four-step guide to being green:

       Reduce the amount of things you use and throw away.

      When you use less of something, you do a good thing for the earth. For example, if you take a shorter shower, it means that you will use less water and less fuel(燃料).

      Reuse things when you can.

      Sometimes people call our society a "throwaway society". That means that we're quite used to throwing away old things and buying new things. Many times, even if you no longer need something, someone else just might need it. For example, if you are in Grade Two, why don't you give your used books to a student who is in Grade One now?

      Recycle bottles, paper, books and even toys.

      Recycling is easy. Many people will pick up your recycled things right in front of your house. Tell your mom or dad that you want to recycle things and help remind others about which things can be washed and recycled.

      Enjoy the earth--walk in the woods, plant a tree, and eat some of the delicious food that it produces.

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