有一块被篱笆围起来的农田，已知篱笆形状是个三角形，三边长分别为51、28和42米，其周长为____米。

在下列长度的各组线段中，能组成直角三角形的是（        ）。

      Years ago, I lived in a building in a town. There was another building across from mine, and it was only a few metres away. There lived a woman whom I had never met. I could see her sit by the window each afternoon, drinking or reading.
     Several months later, I noticed her window was very dirty. Everything was not clear through the window. I wondered why the woman didn't wash her window.
      One sunny morning, I decided to clean up my apartment, including washing my windows. Late in the afternoon when I finished the cleaning, I sat down for a rest by the window. What a surprise! The woman sitting by her window was clearly seen! Her window was clean! Suddenly, I realized I had made a mistake. I was watching her through my dirty window all the time!
     That was quite an important lesson for me. Since then, whenever I wanted to judge （判断） someone, I asked myself first, "Am I looking at him through the dirty window of my heart? ”Then I try to clean the window of my own world so that I may see the world clearly.