重点讲解：
1. break down （使）（物质）分解；
Over time, the protein in the eggshell breaks down into its constituent amino acids.
时间久了，蛋壳中的蛋白质就会分解为其构成成分氨基酸Cv;b%NBaeCp1HknQM)qT。
2. at least 至少，起码；
Success was assured and, at least to start with, the system operated smoothly.
成功有保证了，至少该系统一开始运行得挺顺利~N,R3BG1.BCvzN。
3. clean out 彻底清理(橱柜、房间、容器等)；把…打扫干净；
Mr. Wall asked if I would help him clean out the bins.
沃尔先生问我能不能帮他把各个箱子彻底清理一遍36phHPi6)GWB。
4. come into contact with 接触；遇见；
Common sense tells us that most fuels can burn only when they come into contact with air.
常识告诉我们，大多数燃料只有接触空气时才能燃烧4b^%Y%B!m;!mzk。