I got the new NEC book. Try to find where in the book contains the provisions regarding two-prong electric outlets in old houses (prior to 1960s).

If the houses are not upgraded and outlets remain the same as the before (two-prongs), any mandates require the upgrades or changes to meet today's electric code.

Any easiest way to do so without rewiring the entire house that seems impossible or cost prohibitive? replace two prongs with GFCI outlet on every signle one?

City requires that all electric outlet must be Either grounded, two-prongs or GFCI. Any ideas?