Early During Earth's History What Two Things Contributed Heat That

Multiple Choice

Early during Earth's history what two things contributed heat that led to the internal melting and formation of the core?

A) a hotter proto-sun and the burning off of Earth's early hydrogen atmosphere
B) tidal forces and friction between moving unconsolidated meteorite debris
C) kinetic energy of impacts from nebular debris and decay of radioactive elements
D) chemical reactions between early unstable elements