物理学中常用一些模型来形象地描述一些客观存在的物质，例： ____可以用来表示光的传播路径和方向；磁感线可以用来表示 ____的大小和方向．

下列不属于哺乳动物下丘脑功能的是（　　）

根据短文内容，选择正确答案。
Hello, friends!
    My name is Zhou Dan. I'm a Chinese girl. I'm twelve. I'm from Zhengzhou, China. Do you know Zhengzhou? It's in the middle of China. I'm in No. 8 Middle School. There are about 900 students and 50 teachers in our school. It is a good school in Zhengzhou: I'm in Class 2 Grade 7. There are 49 students in our class: 29 girls and 20 boys. My English teacher is Miss Zhao Dan. Our names are almost the same, right? She is nice to me. We're good friends. I like English, and I like music, too. I want to find a pen-friend. Please write to me.
                                                              Yours,
                                                            Zhou Dan

下列各组二次根式中，可化为同类二次根式的是(     )

在水平桌面上，有两个相同圆柱形容器，内盛相等质量的盐水．将同一鸡蛋分别放人其中，鸡蛋静止时如图所示．鸡蛋在甲、乙两杯中所受浮力分别为F₁和F₂，盐水对容器底部压强分别为p₁和p₂，则（   ）