一句话的分析This he says presents cleanup crews with an enormous t

消灭零回答
这是Obama Warns Oil Spill Will Substantially Impact Economy中的一句话吧.结构是比较松散呢.
首先he says应该是插入语,可以放在句首,海军将领 Allen说
接下来句子前半部分很好理解了.This presents cleanup crews with an enormous task 意思是这（漏油）对清理人员是项巨大的工程,as they deal with what he calls an "enemy that changes,"是表原因从句,因为他们要对付的是他称为“会变化的敌人”.其中what he calls an "enemy that changes是名词从句,enemy that changes是指漏油,在海上不会静止而是随着海流变化.
后半句麻烦一点,and 前省略了this presents, 完整的为This presents an impact on wetland areas as part of long-term environmental effects that will be felt for years.这会给湿地带来持续多年的长期环境影响.that will be felt for years 定语从句,修饰effects. as这里当“作为”讲.