Suppose an economy produces two goods: food and machines. This economy always operates on its production possibilities frontier. Last year, it produced 50 units of food and 30 machines. This year, it is producing 55 units of food and 33 machines. Which of the following would NOT explain the increase in output?

a)A reduction in unemployment

b)An increase in the labor force

c)An improvement in technology

d)An increase in worker productivity