The audience for the new opera, an inventive rendition of Wagner’s Tristan and Isolde, was clearly enthralled by the show for the attendees paused for some moments before applauding vigorously at its conclusion.
Option (A)
Audience is what’s called a collective noun because, like jury or family it describes a group of people that functions as a singular subject; one says the family is rather than the family are.
Therefore, the singular was is the correct verb for audience and you can eliminate (B) and (C).
Next, you have to decide among for the attendees, for they, and as is clear since its attendees.
(D) has a pronoun error since they has no clear referent. The singular audience wouldn’t work as the referent, and the sentence doesn’t provide us with any other options.