An Indication of How Barriers to Entry Can Break Down

An indication of how barriers to entry can break down over time, particularly as consumer preferences change and as technological change makes possible the introduction of new products and new ways of making products, is seen by the

A) high failure rates among monopolistically competitive firms such as restaurants, but rarely seen in oligopolistic industries.
B) virtual disappearance of firms that are monopolies.
C) growing number of oligopolistic firms that have become monopolistically competitive.
D) high failure rates even among large oligopolistic firms.