90%
Complete the fantasy novelist's draft by selecting the most dramatic (and grammatically correct) phrasing for her epic climax.
_________________________ the dragon was so friendly, the brave knight wouldn't have brought her giant, enchanted flyswatter to the cave.
Such __________________________________________ that the royal guards immediately put down their swords and invited it for afternoon tea.
Had she known
This is a third conditional sentence with inversion. By dropping "If", we must invert the subject and the auxiliary verb ("Had she known" instead of "If she had known"). "Did she know" is incorrect because the main clause uses "wouldn't have brought", requiring a past perfect condition.
was the beast's polite demeanor
When a sentence begins with "Such" to emphasize extent or degree, it is followed by the verb "to be" and then the subject (Such + be + noun phrase). "Such was the beast's polite demeanor" correctly applies this inversion rule.