根据表格内容，选择最佳答案。    How time flies! The 9th graders are going to graduate soon. We invite them to write about their school memories.
    Let's share some of them.             
—Ms. Rosen
Name: Brita
Favourite memory: Moving to this school last year and meeting new friends. Unpleasant memory: Being the “new girl”. Favourite teacher: Ms. Rosen. I like her interesting classes. Advice: School can be fun if you do your best.Name: Jay
Favourite memory: School trips. Singing competitions. Unpleasant memory: Project homework. Favourite teacher: Ms. Williams. She treats every student equally. Advice: Work hard and fun will come.Name: Rocky
Favourite memory: Meeting new friends. The weekends. Unpleasant memory: Tests. Favourite teacher: Mr. Taylor. He helps me with my lessons. Advice: Once you fall behind, keep trying till you catch up.Name: Angel
Favourite memory: Being with new people. Fun classes. Unpleasant memory: The loss of a new watch. Favourite teacher: Ms. Rosen. She helped me through hard times. Advice: Hard work brings success.

下列有关物质分类或归类正确的是                                             （   ）
①混合物：盐酸、漂白粉、氯水、水银②化合物：CaCl₂、NaOH、HC1、HD
③电解质：明矾、石膏、冰醋酸、氯化银④同素异形体：C₆₀、C₇₀、金刚石、石墨
⑤放热反应：盐酸与氢氧化钠、碳与二氧化碳高温化合成一氧化碳、甲烷燃烧

下图为世界及四个大洲城市化发展统计图，读图回答下列各题。

以下家庭食品制作中，发生了化学变化的是（   ）

研究燃料的燃烧和对污染气体产物的无害化处理，对于防止大气污染有重要意义．