Answer the following question given this paragraph: Einstein's equation helps scientists understand what happens in nuclear reactions and why they produce so much energy. When the nucleus of a radioisotope undergoes fission or fusion in a nuclear reaction, it loses a tiny amount of mass. What happens to the lost mass? It isn't really lost at all. It is converted to energy. How much energy? E = mc 2 . The change in mass is tiny, but it results in a great deal of energy. Q: Einstein's equation helps scientists understand what happens in nuclear reactions and why they produce so much what? A:

[A]. light;
[B]. food;
[C]. hydrogen;
[D]. energy;
[D].