Final answer:
The claim that Gregorian chant was first notated in the eleventh century but is older is true. These chants existed before being notated on a four-line staff, having been traditionally passed down orally. The correct answer is option a) true.
Step-by-step explanation:
The statement that Gregorian chant was first notated on a four-line staff in the eleventh century, but is in fact much older, is true. Gregorian chants are a form of plainchant or plainsong associated with the liturgical music of the Western Church. Prior to the eleventh century, these chants were passed down orally. The development of a notational system on a four-line staff in the eleventh century allowed for these chants to be written down and preserved, although the musical tradition itself predates this notational system. Moreover, during the Medieval period, particularly the high medieval era, a shift toward polyphonic genres such as motets and madrigals began to surface, contrasting with the monophonic nature of Gregorian chant.