A student compares the C-O bonds in four species: carbon monoxide ($\text{CO}$), carbon dioxide ($\text{CO}_2$), the formate ion ($\text{HCOO}^-$) and the carbonate ion ($\text{CO}_3^{2-}$). In each ion all the C-O bonds are equal, because the ion is a resonance hybrid. Which order of C-O bond length, shortest first, is correct?