轻质带正电小球甲靠近轻质小球乙后，两球相互排斥，则小球乙(   )

如图，矩形 $OABC$ 中， $OA$ 在 $x$ 轴上， $OC$ 在 $y$ 轴上，且 $OA=2$ ， $AB=4$ ，把 $\Delta ABC$ 沿着 $AC$ 对折得到 $\Delta AB\text{'}C$ ， $AB\text{'}$ 交 $y$ 轴于点 $D$ ，则 $B\text{'}$ 点的坐标为____．

根据下图所示，其中关于罗马法的说法错误的是（   ）
                        

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

下列物质一定有固定熔沸点的是