The correct answer would be A. The agent of metamorphism that would cause for the overall composition of a rock to change would be hydrothermal solutions. These solutions contain mineral substances that are dissolved in the hot water. When in contact with a rock, the minerals may change the composition of the rock.
Is the question multiple choice?
Answer: Principle of Original Horizontality.
According to the principle of original horizontality all rock layers are horizontal in nature and this is specific to sedimentary rocks. The younger sediments remains in the top layers and older ones remains at the bottom. These sediments accumulate in horizontal and parallel layers and becomes compact to form rocks in the end.
