Mark: The decongestant drug Zokaz was discontinued by its manufacturer because long-term studies revealed that it increased the risk of heart attack. Qualzan, another decongestant, works by essentially the same physiological mechanism as Zokaz. So Qualzan probably also increases the risk of heart attack.

Kathy: The decongestive effects of the two drugs do stem from the same physiological mechanism. But since they are different chemically, the two drugs probably have different side effects.

Which one of the following is a technique of reasoning used in Kathy’s response to Mark?