Final answer:
The drop in demand for the USPS services is due to the rise of digital communication, leading to a decrease in mail volume and raising concerns about the USPS's financial future. The most relevant works cited entry is the 'Fiscal Year 2013 Integrated Plan' from the USPS itself.
Step-by-step explanation:
The decline in demand for postal services correlates with a change in communication preferences that shifted from traditional mail to digital platforms such as email and social media. As indicated in the facts, this has led to a significant decrease in the volume of mail handled by the United States Postal Service (USPS). The question explores how these changes in consumer behavior have affected the supply and demand dynamics of the USPS, hinting at the potential impact on its financial sustainability and continued viability.
Concerning the works cited entries, the excerpt closely relates to the statistical and financial data likely contained within the first citation, "Fiscal Year 2013 Integrated Plan. U.S. Postal Service, Feb. 2014." This document would provide comprehensive information about the USPS's operations, including mail volume and financial performance, thus relating to the subject matter described in the excerpt.