如图，在平面直角坐标系中，点A，B的坐标分别是（﹣3，0），（0，6），动点P从点O出发，沿x轴正方向以每秒1个单位的速度运动，同时动点C从点B出发，沿射线BO方向以每秒2个单位的速度运动．以CP，CO为邻边构造□PCOD．在线段OP延长线上一动点E，且满足PE=AO．

（1）当点C在线段OB上运动时，求证：四边形ADEC为平行四边形；

（2）当点P运动的时间为$\frac{3}{2}$秒时，求此时四边形ADEC的周长是多少？

在动摩擦因数μ=0.2的水平面上有一个质量为m=1kg的小球，小球与水平轻弹簧及与竖直方向成θ=45^o角的不可伸长的轻绳一端相连，如图所示，此时小球处于静止平衡状态，且水平面对小球的弹力恰好为零，当剪断轻绳的瞬间，取g=10m/s²，则：此时轻弹簧的弹力大小____N，小球的加速度大小 ____  m/s²

根据短文理解选择正确答案。

      In 2002, I wrote a letter for my future self with instructions not to open until my birthday in 2014. It is 2014 now. Yesterday was my birthday and I opened it. This is what it said:

Dear Sherri,

         By the time you read this, you will be 30. At the age of 18 I had many dreams about you. Right now I hope you have traveled and seen everything you've always wanted to, boat in Canada and abroad, maybe you have even settled down somewhere in France, and maybe you are working in the field of art. I hope you’re married to Gwynn—the man of your dreams. You'll probably have two children—a girl and a boy.

        If everything goes okay, you'll be living in France in a big house in a small town with Gwynn and your two children. You are doing research in painting. Gwynn will be a computer programmer and you will be doing all right for yourselves.

However, if things don't go according to plan, I wish you love, happiness and joy.

                                                                                                  Love,

                                                                                                       Sherri “18”

       When I read this, I was surprised. So much of what I wanted has come true.

       I did travel to a few more places in Canada. I've traveled to the UK, Australia and Egypt. I have been living in France for nearly 4 years in a big house, in a small suburb（郊区）, in a major city. I am an art teacher in a university. I have two lovely kids.

       But not everything went as what I hoped. I married a man named Tom Rees, and he is an excellent artist. We are doing all right for ourselves.

       I find it cool how the dreams of a young girl can become a grown woman's reality(现实 ).