Final answer:
Palestrina's Missa Papae Marcelli is based on pre-existing material and exhibits post-Tridentine characteristics in its text setting.
Step-by-step explanation:
Palestrina's Missa Papae Marcelli is a musical composition based on pre-existing material. Specifically, it is based on a freely composed motet by Jacquet de Mantua called 'Salve Regina.' This motet served as the basis for the opening section of the Mass, known as the 'Kyrie.'
The post-Tridentine characteristic of the Mass can be most easily perceived in its use of clear and intelligible text setting. This is a direct response to the reforms of the Council of Trent, which aimed to ensure that the words of the Mass were clearly understood by the congregation. In the 'Gloria' section of the Mass, for example, Palestrina emphasizes the text by using homophonic textures and simple melodies.