Step 1: Recall core structural elements.
Group structure typically comprises roles, norms, status/positions, communication patterns, and cohesion.
Step 2: Compare options.
Role and Norm are canonical elements. Prestige is more of an {individual reputation} or esteem, not a structural building block defining the group’s formal patterning (status is the formal element, not “prestige”).
Step 3: Conclude.
Thus Prestige is the best “not an element” choice.
\[
\boxed{\text{Option C}}
\]