Sacred music can be understood in a more limited sense, denoting music of a classical nature inherent in the Judeo-Christian tradition. Or be perceived in its broadest meaning, referring to all music performed in the ceremonies of any and all religions.
Researchers disagree about what sacred music really is. It is generally conceptualized as non-profane musicality, created to animate human feelings of the nature of the sacred and spirituality. It is worth remembering that a song composed by a religious author does not necessarily transform it into sacred music. Therefore, although all sacred musicality is spiritual, not all religious composition is a sacred song. It must have an aura of holiness.
The use of this term was registered for the first time in the Medieval Era, when it was concluded that it was necessary to develop a specific musical theory for the songs performed in masses and in the worship of God. Its most remote expression is Gregorian chant, a musical genre of a vocal nature, composed of a single melody.
The correct answer is C. church.
Music and the minds of people during the Middle Ages were mostly influenced by religion, the church. Secular music was still not a thing - it refers to worldly music, not related to religion. Musical instruments were used to perform music, but they did not actually inspire it. Humanism came after the Middle Ages - the Middle Ages lasted until the 15th century, and humanism started in the 15th, 16th centuries.
However, church was omnipresent at the time - everyone was religious, and if they were not, they were considered heathens. Therefore it is only natural that religion would influence most spheres of life during the Middle Ages.