GMAT Critical Reasoning (CR) | Re: Our city's campaign to persuade parents to have their children vaccina

Yuriko: Our city's campaign to persuade parents to have their children vaccinated ought to be imitated by your city. In the 16 months since the enactment of legislation authorizing the campaign, vaccinations in our city have increased by 30percent.

Susan: But the major part of that increase occurred in the first 6 months after that legislation was enacted, right after your city's free neighborhood health clinics opened, and before the vaccination campaign really gotgoing.

In responding to Yuriko, Susan does which one of the following?