Answer: Option (C) is correct.
Explanation:
Constant returns to scale production function: When there is an increase in inputs (i.e capital and labor) as a result output increases by the same proportion.
For example: If the amounts of equipment and workers are both doubled in the production of bread then as a result the output of bread also doubled.
Suppose the capital and labor increases by 10% then as a result output also increases by 10%.