Explanation:

A static list is most suitable in this scenario because it does not update automatically based on new criteria. When prospects meet the criteria of having no activity in over 90 days, they can be added to the static list and subsequently enrolled in the re-engagement program. Once they are in the program, even if they become active again, they remain part of the list and continue through the nurturing steps. Dynamic lists, on the other hand, update automatically and could remove prospects who re-engage, interrupting the nurture flow. Therefore, a static list ensures stability and consistency in prospect treatment throughout the re-engagement effort.