gwd-7-5我怎么越看越晕？？？

Exposure to certain chemicals commonly used in elementary schools as cleaners or pesticides causes allergic reactions in some children.  Elementary school nurses in Renston report that the proportion of schoolchildren sent to them for treatment of allergic reactions to those chemicals has increased significantly over the past ten years.  Therefore, either Renston’s schoolchildren have been exposed to greater quantities of the chemicals, or they are more sensitive to them than schoolchildren were ten years ago.

Which of the following is an assumption on which the argument depends?

1. The number of school nurses employed by Renston’s elementary schools has not decreased over the past ten years.
   
2. Children who are allergic to the chemicals are no more likely than other children to have allergies to other substances.
   
3. Children who have allergic reactions to the chemicals are not more likely to be sent to a school nurse now than they were ten years ago.
   
4. The chemicals are not commonly used as cleaners or pesticides in houses and apartment buildings in Renston.
   
5. Children attending elementary school do not make up a larger proportion of Renston’s population now than they did ten years ago.

答案居然是C，我怎么越看越觉得说反了

原文说：在过去10年里敏感的孩子所占比例大幅增加，而结论说既不是化学物质增加了也不是学生更加敏感了，要找假设

而C却正好说：现在有敏感现象的孩子不象10年前那样喜欢跑校医疗室了，这是结论需要的假设吗？基于这样的假设，看病孩子应该越来越少呀，孩子有病都不喜欢往医院跑，它又怎么能说比例比10年前增加了呢？？？？脑子一圈问号，请好心人帮忙敲敲清醒

本文说导致过敏的孩子越来越多的原因可能有两个：孩子周围的化学物质越来越多或者孩子们越来越敏感了。

谢谢！