When a tax on a good is enacted,

A、buyers and sellers share the burden of the tax regardless of whether the tax is levied on buyers or on sellers.;
B、buyers always bear the full burden of the tax.;
C、sellers always bear the full burden of the tax.;
D、sellers bear the full burden of the tax if the tax is levied on them; buyers bear the full burden of the tax if the tax is levied on them.