Why would the government require rationing? A. To regulate the value of the dollar
B. To limit purchases
C. To establish trade barriers
D. To improve profits

B to limit purchases

Explanation: A good example of this would be WW2 when supplies worldwide were dwindling. The US and many other countries had to resort to rationing to make sure everyone had at least some food and so that a small amount of people didn't hoard it all.  

basic principles: federalism, separation of powers, checks and balances, judicial review, representative democracy, limited government, rule of law, individual rights and responsibilities, consent of the governed, majority rule, popular sovereignty, equal protection.