challenge: What was the main issue decided by the Supreme Court in United States v. Beach (1945)?
  
  A. The applicability of the Mann Act to human transportation within state borders
  B. The jurisdiction of the District of Columbia in cases involving prostitution
  C. The scope of the Mann Act's prohibition on human transportation for prostitution within the District of Columbia
  D. The constitutionality of the Mann Act's provisions on interstate commerce
  Answer: 