In the Oil Tanker Industry,large Companies Have Lower Risk and Are

In the oil tanker industry,large companies have lower risk and are able to optimize vessel utilization.If consolidation allows companies to lower their long-run average total costs,this is an example of:

A) the opportunity costs of mergers.
B) the increase in utility of managers by being able to control larger companies.
C) the dangers of oil tankers to the environment.
D) economies of scale in the oil tanker industry.
E) the law of diminishing returns.