All of the Following Except One Are Valid Statements Concerning

All of the following except one are valid statements concerning the debate about oligopolies and efficiency.Which is the exception?

A) Oligopolies are often very large and this creates an environment that is conducive to research and technological change.
B) The barriers to entry in an oligopoly industry encourage research.
C) Oligopolies usually achieve productive efficiency.
D) Because of the barriers to entry in oligopoly industries,oligopolies are likely to become complacent and lose their competitive edge.