Senator Rand Paul, a Republican from Kentucky, questions witnesses during a Senate Permanent Subcommittee on Investigations hearing in Washington, D.C., U.S., on Tuesday, May 21, 2013. Apple Inc. Chief Executive Officer Tim Cook will face off against U.S. senators leveling accusations the iPhone maker has created a web of offshore entities to avoid paying billions of dollars in U.S. taxes. Photographer: Andrew Harrer/Bloomberg via Getty Images