Which two textures are in "Viderunt omnes" by Pérotin?

a monophony and polyphony

b homophony and monophony

chomophony and polyphony

d homophony and homorhythm

Notre Dame school organum is referred to as Viderunt Omnes, and organum alludes to the use of polyphonic texture in sacred music, which began with parallel melodic lines moving very closely, this practice was used basicaly to make monophony more attractive, and particularly to enhance monophonic Gregorian chants when everybody was singing the same melodic line; Pérotin's piece combines both textures. Therefore the answer would be a).

monophony and polyphony