Over the Past Two Decades, Logistics Costs as a Percent

Over the past two decades, logistics costs as a percent of the U.S. gross domestic product GDP) have:

A) been extremely volatile due to international events.
B) increased due to transportation deregulation and technology investments.
C) declined due to deregulation, technology investment, and e-commerce.
D) doubled due to growth in international sourcing.
E) remained constant due to a stagnant global economy.