Which of the following is generally true regarding U.S. taxation of nonresident aliens?

	a.	A nonresident alien is never subject to tax in the U.S.
	b.	A nonresident alien is deemed to have a U.S. trade or business if he performs personal services in the U.S.
	c.	A nonresident alien is generally taxed on U.S. source income
	d.	All of the above
	e.	Both B and C