[求助]求解几道逻辑题阿~~

The number of people diagnosed as having a certain intestinal disease has dropped significantly in a rural country this year ,as compared to last year. Health officials attribute this decrease entirely to improved sanitary conditions at water-treatment plants,which made for cleaner water this year and this reduced the incidence of the disease.

Which of the following ,if ture, would most seriously weaken the health officials' explanation for the lower incidence of the disease?

A.Many new water-treatment plants have been built in the last five years in the rural country.

我选的是这个，理由是觉得这个water-treatment在过去的五年里都在这个乡间城镇里，只有去年环境改善，也就是说，这部是w-t的功劳，从而削弱了原文

B...

C.Beacuse of new diagnostic techniques ,many people who until this year would have been diagnosed as having the intestinal disease are now correcly diagnosed as suffing from intestinal ulcers

这是正确答案。。。不明白为什么

看我的解释你是否满意：

官员认为，相比去年得病的人的数量下降主要是归功于在过去5年中建立了很多水处理厂，这个能理解吧。但是，他们的问题是：以下各项如果成立，哪项最不能/或者翻译成削弱(weaken)这些官员的解释。因此，选择C is correct. the key point for this question is to understand the word "weaken"

hope my explanation can help you understand.

good luck

A说的变化发生在5年前，无法解释今年和去年的区别。

C 说由于新技术，明显的他因削弱