Which of the following is not correct?
a. with a growth rate of about 2 percent per year, average income per person doubles about every 60 years.
b. in some countries real income per person has changed very little over many years.
c. across countries there are large differences in the average income per person. these differences are reflected in large differences in the quality of life.
d. the ranking of countries by average income changes substantially over time.

David paid $975,000 for two beachfront lots in coastal south carolina, with the intention of building residential homes on each. two years later, the south carolina legislature passed the beachfront management act, barring any further development of the coast, including david's lots. when david files a complaint to seek compensation for his property, south carolina refuses, pointing to a passage in david's own complaint that states "the beachfront management act [was] properly and validly designed to south carolina's " is south carolina required to compensate david under the takings clause?