Ben N. Jerry prefers to keep his $10,000 retirement savings buried in the backyard. After an increase in the price level, Ben reduces the amount of goods and services he wants to purchase. Ben's rationalization, that now his retirement savings won't buy as much, is consistent with which explanation of the aggregate demand curve's negative slope?

A shift of the supply curve of oil raises the price from $70 a barrel to $80 a barrel and reduces the quantity demanded from 40 million to 38 million barrels a day. You can conclude that the

A) demand for oil is elastic. B) demand for oil is inelastic. C) supply of oil is elastic. D) supply of oil is inelastic.

In a perfectly competitive market ________

A) the goods purchased are assumed to be standardized products B) prices adjust quickly to equilibrium C) buyers and sellers are price takers D) all of the above E) none of the above