What can be used to make complicated concepts and systems easier to study and understand? A. prototypes
B. samples
C. models
D. graphs

C. models

Explanation:

Models have usually used to simplification the harder subjects, and make it easier to work with.

An example of this is when you do the math for a car moving in the street, where you suppose that the car has an easy shape, like a box, you ignore things like air resistance and such.

Models are used in almost every field of physics, especially in the experimental field, where having a lot of variables is a problem, so the scientist develops models where some of the variables can be ignored, and in this way, the experiment and the math are easier.

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.