Statement (A) : Difference in the energy between hybrid and the most stable resonance structures is called resonance energy.

Statement (B) : are canonical structures.

Statement (C) : ${\text{CO}}_3^{-2}$ ion exhibits resonance phenomenon.

Definition of resonance energy: The difference in the energy between hybrid and the most stable resonance structure is called resonance energy.

 Resonance structures of Benzene:

Resonance structures are also called canonical structures.

Resonance structures of carbonate ( ${\text{CO}}_3^{-2}$ ) ion:

So, ${\text{CO}}_3^{-2}$ ion exhibits resonance phenomenon.