Identify more than one correct resonance structure of carbon dioxide from the ones given below:

a.  ${}^{-}\mathrm{O}-\mathrm{C}={\mathrm{O}}^{+}$

b.  $\mathrm{O}=\mathrm{C}=\mathrm{O}$

c.  ${}^{-}\mathrm{O}\equiv \mathrm{C}-{\mathrm{O}}^{+}$

d.  ${}^{-}\mathrm{O}-\mathrm{C}\equiv {\mathrm{O}}^{+}$

Choose the correct option: