This question is fairly easy to answer since describing a room as "pure" sounds odd and that's why I knew right away that I had to look for another suitable replacement for this word so that the sentence grammatically correct.
The word concentrated sounded too clinical for this sentence, therefore I chose option C since it captured what the sentence was trying to say.
![[Literature] Johann Gottlieb Fichte: The Vocation of Man #14/65](/assets/noimage.svg)