Canonical Structures and Resonance

Lewis / Kekulé structures A through D are constitutional isomers having the molecular formula CN2H2. The remaining structures include canonical formulas which should be incorporated in a resonance description of these four compounds. There is also at least one formula that represents a fifth constitutional isomer of CN2H2.

Enter appropriate letters (E through L) in each answer box.
       
This script written by William Reusch, Dept. of Chemistry, Michigan State University. Please send comments and corrections to whreusch@pilot.msu.edu.
The "View Answer" part of this problem does not function using Internet Explorer ver.3 and earlier.