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-underset(CH_(3))underset(|)overset(CH_(3))overset(|)C-C_(6)H_(5)`