GMATprep 里面关于Deficit和currency decline关系的题目

希望高人指点一下，实在看了半天还不知道题目说什么：（ 这个句子很奇怪啊

The recent decline in the value of the dollar was triggered by a prediction of slower economic growth in the coming year. But that prediction would not have adversely affected the dollar has it not been for the government's huge budge deficit, which must therefore be decreased to prevent future currency declines.

请问画线的部分是什么一是啊？？？？怎么连句子的渭语我都不知道是哪个阿：（