What is a key factor (or factors) for a promoter in selecting an opening act to perform before a headliner?

a. None because promoters don’t select opening acts
b. Selecting compatible music and not overshadowing the headliner
c. Selecting a local act with a big following and no concern for music compatibility
d. Always selecting mellow music to relax the audience before the headliner

b. Selecting compatible music and not overshadowing the headliner