SAT Boundaries Question

Reena Esmail's classical composition “Summitless Mountains” incorporates a raag, a melodic framework used in Hindustani classical music, called Raag Chandrakauns. Often, interplay between the raag's designated vadi and samvadi (the first-and second-most important notes, respectively) and its prescribed melodic sequences an unsettled mood. Which choice completes the text so that it conforms to the conventions of Standard English?