如图是课本中的几个实验：

 一个条形橡皮擦放在水平桌面上，下列说法：
①它的硬度大于铁的硬度；    ②它的导热性比铜的导热性差；
③使用后，其密度保持不变；  ④若把它放在水中，一定浮在水面上；
⑤无论怎样放置，它对桌面的压强都相同。合理的是(    )

春节是传统的节日．在外地工作的人们会乘坐各种交通工具回家与亲人团圆．

①航空旅行舒适快捷．制造飞机轮胎的主要材料是　 ____　（填字母）．

a．铝合金           b．橡胶            c．玻璃

②铁路是主要的交通工具．建设铁路需要大量水泥．工业上生产水泥的主要原料是石灰石和　 ____　 （填字母）．

a．黏土            b．纯碱            c．石英

③轮船也是重要的交通工具．为保护钢板不受腐蚀，在船尾（如图）钢板上镶嵌的金属块是　 ____　（填字母）．

a．铜块             b．锌块        c．锡块．

阅读短文，判断正误。

Dear Joe,

How are you? My sister and I are having our holiday. Yesterday we went to the library. We got there by bus. We read storybooks and had lunch there. The food was delicious. It was cheap, too. We went shopping in the afternoon. I bought a pair of shoes. I was very tired. We are planning to learn skating and do many other things during the holiday. We are sure we'll have a good time.

How about your holiday? Please write to me soon.

Miss you.

Alice