The sun is the major external source of energy, and the primary internal energy sources are the decay of radioactive isotopes and the gravitational energy from the earth's original formation.
(The sun; is; the major external source of energy) (the primary internal energy sources; are; the decay of radioactive isotopes and the gravitational energy from the earth's original formation)
The sun the primary internal energy sources
is are
the major external source of energy
the decay of radioactive isotopes and the gravitational energy from the earth's original formation