Final answer:
Thirty retired people going on a two-week tour of Europe together represent a tour group, which differs from sports teams, book clubs, cooking classes, or formal organizations. This is because the main purpose of their assembly is the shared experience of travel.
Step-by-step explanation:
The type of group that thirty retired people going on a two-week tour of Europe together represent would most accurately be classified as c) A tour group. This collection of individuals comes together for the shared experience of traveling and exploring new places. In contrast to a sports team, which is organized around playing and competing in sports, or a book club, which centers around the discussion of literature, a tour group is specifically organized for travel. Additionally, a cooking class is designed for teaching and learning culinary skills, which is different from the purpose of a tour group.
From this information, it is also clear that a tour group does not meet the definitions of a formal organization, such as a normative organization like a book club or a church youth group as it has a different collective purpose.
Neither is it an interest group defined by advocacy or shared goals in a specific area of economic, labor, civil rights, or demographic interest. Lastly, a tour group is distinct from the concept of a reference group, which is a group whose values, norms, and beliefs influence an individual's behavior.