A lot of collective nouns can be singular or plural. We consider them as plural when we are thinking of a group of people who can think and act independently. We use the singular when we consider it as a single unit. "The government (various ministers with different opinions) are considering the problem"; "The government has fallen" (it stands or falls together).
As for audience I would tend to use it more in the singular than in the plural. In the example, A report is a communication needed and directed by an audience. "an audience" either exists or doesn't exist. It can't exist one person at a time, so we consider it as a single unit.
A plural use could be "The audience were not happy with the performance", meaning the individuals making up the audience were not happy. But even here I think the singular sounds OK.

showbu wrote: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 t its conclusion.

A. was clearly enthralled by the show for the attendees

B. were clearly enthralled by the show for they

c. were clearly enthralled by the show as they

d. were clearly enthralled by the show for they

e. was clearly enthralled by the show as is clear since its attendees