素材库（三）  

出　　处：《考试与评价（英语外研新标准初一版）》2009年第3期30-30,共1页

摘　　要：Keep It Clean s Sometimes a lake looks blue. The water is clean and clear. At other times a lake can look green. What makes a lake turn green？ The answer is chemicals （化学物质）． They get into a lake from factories, farms, and homes.

关 键 词：素材库 OTHER green KEEP look WHAT 化学物质 from 

分 类 号：G434[文化科学—教育学] G633.41[文化科学—教育技术学]