| The number of people diagnosed as having a certain intestinal disease has dropped significantly in a rural county this year, as compared to last year. Health officials attibute this decrease entirely to improved sanitary conditions at water-treatment plants, which made for cleaner water this year and thus reduced the incidence of the disease.
Which of the following, if true, would most seriously weaken the health officials’ explanation for the lower incidence of the disease?
B. Bottled spring water has not been consumed in significantly different quantities by people diagnosed as having the intestinal disease, as compared to people who did not contract the disease.
我想请教一下这个选项为什么错，因为觉得好像自己思路有点偏差 B说，染病的人和不染病的人喝水的数量几乎没差别，那是不是可以说不是因为水的问题导致的疾病下降，那样不是也同样削弱了么？ | 
