城市是人类社会发展的产物,对地理环境影响很大。城市景观对城市气候的影响(   )

宏伟的长城是我国人民智慧和独创性的特征，秦朝时修的长城是为了抵御下列哪个少数民族的进犯（    ）

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

化学就在我们身边，它与我们的生活息息相关．

（1）下表为某食品包装袋的部分说明．

请回答下列问题：

①在饼干的配料中，富含油脂的是____ ；

②配料中可用于腌渍蔬菜的物质是____ ；

③小麦粉中富含糖类，糖类在人体内经过一系列的变化最终转化为水和____ ；

④食用香精中含有香豆素（C₉H₆O₂），香豆素中碳、氢、氧三种元素的质量比为　____ ；

（2）现有H、C、O、Ca四种元素，请选用其中的元素写出符合下列要求的物质的化学式．

①最轻的气体____ ；②“西气东输”中“气”的主要成分____ ；

③人体中含量最多的物质　____ ；④可用作食品干燥剂的氧化物____ ．