This week Wal-Mart is set to announce a major initiative aimed at helping cottonfarmers go organic：it will buy transitional cotton at higher prices， thus helping toexpand the supply of a key sustainable material.
本句的主干是Wal-Mart is set to announce initiative。aimed at helping cotton farmers goorganic为maior initiative的后置定语；冒号之后的内容是对major initiative的具体解释说明，其中thus helping…为状语。
he set to do sth.的意思是“准备好做某事”。如：
They were all set to go when the bell rang.铃 声响起时，他们都准备好要走了。
aim at doing sth.的意思是“企图、力求做某事”。如：
We must aim at increasing tlae profits.我们要力求增加利润。
英语四.级考点归纳：
go除了作不及物动词表示“走，去，前进”等，还可以作系动词：
+ 表示“处于……状态”。如：
I'd rather go hungry than have breakfast.我宁愿挨饿也不吃早餐。
楼主