What features do all of the resonance forms of a molecule or ion have in common

What features do all of the resonance forms of a molecule or ion have in common?
(More than one answer/multiple answers)

a. arrangement of atoms
b. arrangement of electrons
c. atoms present
d. net charge on the molecule or ion
e. formal charge on each atom
f. number of electrons
g. none of these are common between resonance forms

a, c, d and f are true.