Answer:
The correct answer is option C. Polyphony
Step-by-step explanation:
Western plainchant has a central tradition which is known as the Gregorian chant. It is a sacred song which is a form of Latin monophonic and unaccompanied at the Roman Catholic church. It came about mainly in the ninth and tenth centuries in the western and central Europe, followed by its new additions.
As it is clear from the above description, it was a monophonic Latin song. Monophonic means when it only consists of one line of independent symphony. Whereas polyphony means multiple lines of symphonies at the same time, which was not part of the song.