Suppose $Q=f(p)$ denotes the number of barrels of oil sold by a company when the price is $p$ dollars per barrel. $R(Q)$ denotes the revenue earned in millions of dollars for selling $Q$ barrels.

Which of the statements best explains the meaning of $R(f(p))$?

A. The total amount of barrels sold when the overall revenue is $p$ dollars.
B. The total amount of revenue earned for selling $p$ barrels of oil.
C. The total amount of barrels sold when the price of oil per barrel is $p$ dollars.
D. The revenue earned when the price of oil per barrel is $p$ dollars.
E. None of the above