The Primary Principle of the "Neutral" Theory of Natural Selection

The primary principle of the "neutral" theory of natural selection is that

A) evolution is primarily driven by purifying selection against deleterious mutations.
B) advantageous and deleterious mutations play an equal role in evolution.
C) genetic drift by random allele fixation plays a dominant role in evolution.
D) it is impossible to deduce whether observed allele frequencies are caused by positive or negative selection.