Which of the following statements is CORRECT about productivity?

Select one:

a$.$ Productivity measures that use one or more inputs or factors, but not all factors, are called limited productivities

b$.$ Productivity is measured by dividing the average input per period by the total costs incurred

c$.$ Productivity is not production but is concerned with how effectively outputs are produced

d$.$ Productivity can be defined as the mathematical ratio between the input and the output used to achieve an objective