Ⅰ. 用本单元适当的单词补全短语
1. confuse the students使学生迷惑
2. have no regret没有遗憾
3. chemical change化学变化
4. at each stage of production在生产的每个阶段
5. make an important discovery有重大发现
6. keep the soil dry保持土壤干燥
7. reduce pollution and waste减少污染和浪费
8. underline the topic sentence画底线标出主题句
9. skim the passage略读课文
10. make a comment发表评论
11. the root of the problem问题的根源
