鲫鱼是一种常见的淡水鱼类．关于“探究鲫鱼适应水中生活特征”的实验结论，正确的是（    ）

Monday, May 7, Sunny

    I had a pretty good time in Beijing last weekend with my parents and my brother.

    We went to Beijing by train on Friday night and got there on the morning of Saturday. We went to Tian'anmen Square first. There were many people there. We watched the national flag(国旗)go up. Then we went to the Palace Museum. My parents liked it very much, but I thought it was kind of boring. After lunch, we visited the Great Wall. When we got to the Great Wall, it started to rain. The rain made the mountains look very beautiful. We played on the Great Wall and took some photos. On Sunday morning, we visited a Beijing Hutong. Then after buying some things in Wangfujing Street in the afternoon, we went back home. We really enjoyed ourselves.

⑴题完成句子；(2)～(3)题简略回答问题；(4)题找出并写下全文的主题句；(5)题将文中画线句子译成汉语。

①2是8的立方根； ②±4是64的立方根；  ③无限小数都是无理数； ④带根号的数都是无理数．

小静想：白球碰撞后立即静止，被撞的球是以白球撞前相同大小速度运动出去的吗？

通过了解和初步实验，小静发现只有当体积和质量均相同的两球，而且球心在同一直线上相碰时，才可能出现上述现象。为进一步探究，她设计了下述实验方案：

将一个两端翘起、中间水平的轨道固定在水平桌面上，取两个相同的台球A、B，将B球静置于轨道的水平部分，A球置于轨道左端斜面上某处，测出该点到水平桌面的高度h₁，如图乙所示，释放A球，撞击后，A球静止，B球向前运动并冲上轨道右端斜面能到达的最高点，测出该点的高度h₂。通过比较h₂与h₁的大小关系即可作出判断．请你作答以下问题：