甲同学在一根装满水的较长的铁管一端敲一下，乙同学在铁管的另一端能听到三次敲击声．请回答：

（1）按乙同学听到的先后顺序，指出这三次声音分别是什么物质传播的？

（2）简要说明听到三次声音原因？

一个几何体的三视图如图所示，其中正视图和侧视图是腰长为2的两个全等的等腰直角三角形，俯视图是圆心角为 $\frac{\pi }{2}$ 的扇形，则该几何体的侧面积为（   ）

既能发生加成反应，又能发生皂化反应的是（ ）。

地壳中含量最多的金属元素是（    ）

读短文，判断对错。
    Hello, everyone! My name is Kate. I come from France. Now I'm in China with my parents. I'm a student of No. 2 Middle School (第二中学). The teachers there are very friendly (友好的) to me. The students there are friendly, too. I like them very much. Look at that tall man! He's my father. He has big eyes and a big nose. He's handsome. He is a doctor. He often helps people in need. That beautiful woman is my mother. She has long hair and big blue eyes. She's a nurse. My parents and I all like China very much. The Chinese food is very yummy. The Spring Festival (春节) is coming. We will spend (度过) the Spring Festival in Beijing.