One of the most difficult aspects of deciding whether current climatic events reveal evidence of the impact of human activities is that it is hard to get a measureof what constitutes the natural variability of the climate. (TPO10, 38)

我是分界线，大家先自己速读哦。

One of the most difficult aspects (of deciding)(whether current climatic events reveal evidence of the impact of human activities) is that it is hard to get a measure of (what constitutes the natural variability of the climate).(TPO10, 38)托福听力加试算分吗

分析：

这个句子的主干就是： One of the most difficult aspects is that

修饰一：(of deciding) ，介词短语，修饰aspects

中文：确定

修饰二：(whether current climatic events reveal evidence of the impact of human activities) ，宾语从句，

中文：现在气候事件是否揭露了是人类活动影响的证据

修饰三：(what constitutes the natural variability of the climate) ，宾语从句

中文：什么组成了气候的自然可变性

参考翻译：

确定现在气候事件是否揭露了是人类活动影响的证据，其中最大困难之一在于很难去测量是什么组成了气候的自然可变性。

这个句子的主要修饰成分就是从句和介词短语，大家务必想清楚，每一个修饰成分修饰的是什么，才能看清楚这个句子的结构。