What is the term for the genre of western european sacred music that was non metrical, monophonic, and sing from memory by trained musicians?

Medieval music consists of songs and pieces from an era of Western music, including liturgical music (also known as sacred) used for the church, and secular music, non-religious music. Medieval music includes solely vocal music, such as Gregorian chant and choral music (music for a group of singers), solely instrumental music, and music that uses both voices and instruments (typically with the instruments accompanying the voices). Gregorian chant was sung by monks during Catholic Mass. The Mass is a reenactment of Christ's Last Supper, intended to provide a spiritual connection between man and God. Part of this connection was established through music.[1] This era begins with the fall of the Western Roman Empire in the fifth century and ends sometime in the early fifteenth century. Establishing the end of the medieval era and the beginning of the Renaissance music era is difficult, since the trends started in different regions. The usage in this article is the one usually adopted by musicologists.

During the Medieval period the foundation was laid for the notational and theoretical practices that would shape Western music into the norms that developed during the common-practice era. The most obvious of these is the development of a comprehensive music notational system which enabled composers to write out their songs and pieces on parchment or paper. Prior to the development of musical notation, songs and pieces had to be learned "by ear", from one person who knew a song to another person. This greatly limited the geographic spread of songs or pieces. The development of music notation made it easier to disseminate songs and musical pieces to a larger geographic area. However the theoretical advances, particularly in regard to rhythm—the timing of notes—and polyphony—using multiple, interweaving melodies at the same time—are equally important to the development of Western music.

the answer is d . a measurement   how can artists measure the width of the human face to use drawing for correct proportions

hi     (had to add 20 words)