A：绿色化学的核心是利用化学原理对环境污染进行治理
B：自来水可用氯气来杀菌消毒．说明氯气无毒
C：纯碱可用于生产普通玻璃，日常生活中也可用纯碱溶液来除去物品表面的油污
D：从海水中提取物质都必须通过化学反应才能实现
Rick is a good man．He makes birthday cakes in a shop．His cakes are great and have very good prices，so many people buy his cakes．He makes friends with lots of his customers(顾客)．They all like him very much．One evening．he wants to go home，but many of his old customers come in．Rick smiles(微笑)to them，“I am sorry．It is late today．If you need cakes，please come tomorrow．”One of them takes out a nice cake and says to him，“You make so many great cakes for us．This birthday cake is for you．Happy birthday, Rick．”
假如你是生活在距今约7000年长江流域的原始居民，你不可能看到下列哪一现象( )
