17. what does modern physics study?\nmagnetic forces\nnuclear reactions\nheat transfer\nthe theory of…

Brief Explanations:

Modern physics encompasses theories and phenomena that classical physics cannot explain. The theory of relativity, developed by Einstein, is a corner - stone of modern physics. Magnetic forces, nuclear reactions, and heat transfer are more related to classical or specific sub - areas of physics rather than being the defining study of modern physics.

Answer:

D. the theory of relativity