There are many processes talked about in the lecture (and the text) that create a metamorphic rock. which one is the only one that is required in that process?

a. differential stress
b. confining pressure
c. heat
d. hydrothermal activity

b.Confining pressure

Explanation:

They are formed by the confining heat and pressure that they derive from the physical and chemical alteration of the igneous and the sedimentary rocks.  The rocks undergo es a regional metamorphism and involve a larger body of rocks that occur over a wider area. Typically are associated with mountain building and orogenic events and display a distinct band of mineral and colors, which is called foliation. The force that drives these rocks to the various forms are those of the plate tectonics and includes the separating rides and the subducting zone along wit the continental collisions.