Definition: You are given a question on conceptual physics. You are also given 4 answer options (associated with "A", "B", "C", "D"), out of which only one is correct. You need to answer the question by selecting the correct option. You should only answer with the choice letter, not the whole answer.
Input: The equation E = mc^2 indicates that energy
(A)equals mass moving at the speed of light squared. (B)equals moving mass. (C)is fundamentally different than mass. (D)and mass are closely related.

D