<p>The acoustics at the ancient Greek theater of Epidaurus are [so good that] an author's words, even when whispered, are auditory to those siting in the last row.</p>
<p>What should "so good that" be corrected to? "so well that" doesn't sound right either..</p>
<p>I don’t see a problem with “so good that.” “auditory,” however, seems problematic: as far as I know, “auditory” cannot mean “audible.”</p>
<p>I misread the answer key, thank you.</p>
<p>Silverturtle is right. I would also add that ‘good’ is an adjective. ‘Well’ is an adverb. The sentence calls for a predicate adjective.</p>