三角形两边长分别为2和4，第三边长是方程x（x﹣4）﹣2（x﹣4）=0的解，则这个三角形周长为（   ）

小红同学为探究R、X、Y和Z四种金属的活动性顺序，进行以下实验．

    Mr. Brown is a teacher. He is from New York, America. He would like（想）to work in China because he likes our country. He thinks Chinese people are very friendly and he likes to live in China. He is happy to work in our school. He likes the school life here. He teaches English. There are 50 students in his class. Mr. Brown is kind. He and his students are good friends, too.
    Now some of Mr. Brown's students play sports on the playground（操场）. Bill and Mike play tennis. Tom and John play ping-pong. The other students play basketball. Mr. Brown is happy to play basketball with them. They have a good time.
阅读上面的短文，根据短文内容，选择最佳选项。   

下列属于从传播环节防治噪声的是(  )

卫星云图上，绿色表示陆地，蓝色表示海洋，白色表示____，白色很浓的地方，天气往往是____。