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.

to treat tumors in the body

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.