The audience's reaction to a play they didn't like can vary, but the most common and appropriate response is:
b. They would leave the theatre.
If the audience doesn't enjoy a play, it's customary for them to quietly exit the theatre rather than disrupt the performance or fellow theatergoers. Options a and c are considered highly disruptive and disrespectful to both the actors and the audience. Option d, complaining to the management, is a more constructive way to express dissatisfaction, but it's typically done after the play has ended, not during the performance itself.