Why were Americans so driven to expand across the continent?

Which of the following accurately describes the workforces of the united states and canada? a. most of the workforce in the united states and canada is employed in the service industry. b. most of the workforce in the united states and canada is employed in the educational field. c. most of the workforce in the united states and canada is employed in manufacturing and mining. d. most of the workforce in the united states and canada is employed in agriculture.