请教GWD 5－第5题

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.