Which of the following best describes 'happenings'?

The correct choice highlights that 'happenings' are unique, spontaneous events that differ significantly from traditional performances. They are characterized by their improvisational nature, bringing together various elements such as theater, music, visual arts, and audience participation in an unpredictable and engaging manner. This allows each occurrence of a happening to be a distinct experience, shaped by the participants and the environment.

In contrast, the other options suggest aspects that do not align with the essence of happenings. For example, fixed performances with strict guidelines imply a level of control and predictability that happens intentionally disrupt. Artworks meant to be viewed quietly in galleries focus on static presentations rather than active, participatory engagement. Lastly, adhering to scripts during a performance suggests a structured format that contradicts the improvisational and fluid character of happenings. Thus, the unique and variable nature of happenings is accurately captured in the selected answer.