The Energy Source That Heats the Low-Density Coronal Gas to Extremely

The energy source that heats the low-density coronal gas to extremely high temperatures is MOST probably:

A) conduction because the chromosphere and corona contain high densities of free electrons that facilitate conduction.
B) rearrangements within complex magnetic field structures that energize the ionized gas.
C) convective currents in the chromosphere that carry hot gas outward from the photosphere.
D) radiative heat from the photosphere that is strongly absorbed by highly ionized atoms such as Fe XIV.