Keto-enol tautomerism is not 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)-CH(CH_(3))_(2)`
D. `C_(6)H_(5)-overset(O)overset(||)(C)-CH_(2)-overset(O)overset(||)(C)-CH_(3)`