Recall the Application About Declining U

Recall the Application about declining U.S. labor force participation since 1999 to answer the following question(s) .
-According to this Application, one explanation for the decline in the U.S. labor force participation rate since 1999 is

A) the decline in the overall population.
B) the increasing number of retiring baby boomers.
C) the increase in immigration to the United States.
D) the increase in outsourcing by U.S. companies.