 Solution

C has the original cyclohexadiene connectivity but trans, rather than cis, adjacent methyl groups. Draw one methyl wedge and the other dash, keeping both phenyl groups at the diene termini. One enantiomer is shown below; reversing both stereobonds gives its mirror image. For the symmetric achiral starting framework under achiral conditions, the two trans enantiomers are not distinguished by this orbital-symmetry argument.