Research Has Shown That Most Economic Profits from Selling a Prescription

Multiple Choice

Research has shown that most economic profits from selling a prescription drug are eliminated 20 years after the drug is first offered for sale.The main reason for the elimination of profits is

A) after 20 years most people who have taken the drug have passed away or are cured of the illness the drug was intended to treat.
B) firms sell their patent rights to other firms so that they can concentrate on finding drugs to treat new illnesses.
C) the quantity demanded of the drug has increased enough that the demand becomes inelastic and revenue falls.
D) after 20 years patent protection is ended and other firms can produce less-expensive generic versions of the drug.