Keto-enol tautomerism is observed in
A. `C_(6)H_(5)-overset(O)overset(||)(C)-H`
B. `C_(6)H_(5)-overset(O)overset(||)(C)-CH_(3)`
C. `C_(6)H_(5)-overset(O)overset(||)(C)-C_(6)H_(5)`
D. `C_(6)H_(5)-overset(O)overset(||)(C)-overset(CH_(3))overset(|)underset(CH_(3))underset(|)(C)-C_(6)H_(5)`