Final answer:
In 2010, about 80% of the U.S. labor force was employed in the tertiary sector, with the remainder split between the secondary and primary sectors.
Step-by-step explanation:
In 2010, the U.S. labor force was predominantly engaged in the tertiary sector, with nearly 80 percent of workers employed in service industries, according to the U.S. Bureau of Labor Statistics. This trend reflects the economic development patterns where advanced economies, like the United States, have a workforce gravitating towards the service sector. While the data provided does not give specific percentages for the secondary and primary sectors in 2010, it implies that the remaining 20 percent would be distributed between those two sectors, with the secondary (manufacturing and construction) typically higher than the primary (agriculture, fishing, and mining).