Which one of the following is least stable resonating structure ?
A. `NH_(2)-overset(O)overset(||)C-O-CH_(3)`
B. `{:(" ".^(Theta)O),(" |"),(overset(o+)NH_(2)=C-OCH_(3)):}`
C. `{:(" O"^(Theta)),(" |"),(NH_(2)-underset(o+)C-OCH_(3)):}`
D. `{:(" O"^(Theta)),(" |"),(NH_(2)-underset(o+)C=underset(o+)O-CH_(3)):}`