Explain How Radioactive Decay Has Always Warmed the Earth from the Inside,and

Multiple Choice

Explain how radioactive decay has always warmed the earth from the inside,and nuclear fusion has always warmed the earth from the outside.

A) Much heat was released as matter coalesced to form the earth.This heat resulted in the production of radioactive isotopes,which still reside within the earth today and are a source of internal heat.Our primary external source of heat is from the fusion of hydrogen within the sun.
B) The inner Earth is made of fissioning heavy elements while the sun is made of lighter fusing elements.
C) Radioactive elements have been within Earth since it was created while the sun is made of fusing hydrogen atoms.
D) All of the above are reasonable answers.