一个经典的削弱题不懂，请帮忙

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

   Which of the following, if true,would most serously weaken the conclusion about how to prevetn future currency declines?

(C) The value of the dollar declined several times in the year prior to the recent prediction of slower economic growth.

(D) Before there was a large budget deficit,predictions of slower economic growth frequently caused declines in the dollar's value.

请问原文第二句是什么意思， had it not been是什么结构？没明白原文的逻辑意思

选项C为什么不对？感觉这是一个有因无果的例子阿。。。谢谢

是虚拟语气。意思是说如果不是因为政府的高额财政赤字，对经济增长缓慢的预测是不会导致美元下跌的。那么什么能够削弱原文的结论呢，

如果有例子可以说明在没有财政赤字的情况下，对经济增长缓慢的预测曾经导致美元下跌，那么不就削弱了么，D选项就是这个意思。

C只能说明即便没有预测，美元也可能下降，但对财政赤字是无关的