Returns to Scale Refers To

Returns to scale refers to:

A) the increase in output that accompanies an increase in one input, all other inputs held constant.
B) a change in a production process that enables a firm to achieve more output from a given combination of inputs.
C) the number of units of increase in output that can be obtained from an increase in one unit of input.
D) the percentage by which output will increase when all inputs are increased by a given percentage.