When the Oxidation-Reduction Reaction Shown Here Is Balanced Using the Smallest

Multiple Choice

When the oxidation-reduction reaction shown here is balanced using the smallest whole-number coefficients, how many electrons are transferred?
Cu²⁺(aq) + Al(s) $\rightarrow$ Cu(s) + Al³⁺(aq)

A) 0
B) 2
C) 3
D) 6
E) 12