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

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

b. Under what circumstances might Michael be considered a resident of the United States? Would such a classification be advantageous? Disadvantageous? Explain.