Which of the statements below about resonance structures is true?

• A. Atoms can be added or removed when drawing one resonance structure to another.
• B. Electrons must always be added when drawing one resonance structure to another.
• C. Only electrons can be moved when drawing one resonance structure to another.
• D. Electrons and atoms can be moved when drawing one resonance structure to another.
• E. Electrons and atoms cannot be moved when drawing one resonance structure to another.