The correct answer is B. Until he truly heard classical music, he never knew that bittersweetness lived in wordless song.
Step-by-step explanation:
The function of adverb clauses is to modify or describe the action in the sentence. In terms of structure, this usually begin with words such as when, after, until, etc that add information about time, reason, way, among others. Also, in terms of punctuation if the adverb clause is placed before the main sentence this is separated using a comma.
This correct punctuation is exemplified in "Until he truly heard classical music, he never knew that..." because the section "Until he truly heard classical music" is an adverb clause introduced by the word "until" and this has been separated from the main sentence "he never knew..." with a comma.