* Gregorian Chant is monophonic, meaning it is sung by a single voice.
* Gregorian Chant is unaccompanied, meaning it is not accompanied by any instruments.
* Gregorian Chant is modal, meaning it uses a particular set of scales or modes.
* Gregorian Chant is responsorial, meaning it consists of a series of verses and responses sung by a soloist and a choir.
* Gregorian Chant is polyphonic, meaning it is sung by multiple voices at the same time.
Therefore, the correct answer is: polyphonic.