Which of the following would cause the labor force participation rate to decrease?

a.There was a decrease in the number of 70-year-old people working by 2,000.

b.15,000 people between the ages of 55-60 who were previously employed have decided to retire.

c.50,000 people who were previously employed have become unemployed.

d.100,000 people who were previously unemployed have now found jobs.