Final answer:
The rise of stadium concerts in the 1970s led to more elaborate stage setups and effects, as artists needed to engage larger audiences in bigger venues.
Step-by-step explanation:
The rise of the stadium concert in the 1970s significantly altered the way groups performed. The correct answer to the question 'How did the rise of the stadium concert change the way groups in the 1970s performed their concerts?' is C) It encouraged more elaborate stage setups and effects.
The vast size of stadiums compared to traditional venues meant performers required more elaborate stage setups, advanced sound systems, and visual effects to engage audiences that were much farther from the stage. These developments led to more dynamic performances and began a trend of concerts as large-scale events beyond mere musical performances.