In which of the following esters the `alpha` - hydrogen is acidic ?
A. `H-overset(O)overset("||")C-OC_(2)H_(5)`
B. `O_(2)N-CH_(2)-overset(O)overset("||")C-OC_(2)H_(5)`
C. `underset(CN)underset(|)CH_(2)-overset(O)overset("||")C-OEt`
D. `Ph-CH_(2)-overset(O)overset("||")C-OEt`