Oliver is a U.S. citizen employed by a multinational corporation at its London office. Oliver is married to Regina, a British citizen, and they reside in England. Regina receives substantial rent income from real estate she owns in western Europe.

a. Must Oliver file a U.S. income tax return?

b. Under what circumstances might Regina be considered a resident of the U.S? Would such a classification be advantageous? Disadvantageous? Explanin.