Which statement regarding oxides is true?
A. CaO is an acidic oxide because Ca2+ acts as an acid when CaO reacts with H2.
B. CO2 is an acidic oxide because CO2 ionizes in H2O and O2- acts as a Lewis acid.
C. MgO is a basic oxide because Mg2+ can act as a Lewis base.
D. Amphoteric oxides behave as acidic oxides in the presence of H3O+.
E. None of the above statements are true about oxides.