For a Firm,what Does "Constant Returns to Scale" Refer to

Multiple Choice

For a firm,what does "constant returns to scale" refer to

A) Short-run average total cost changes at a constant rate as the quantity of output changes.
B) Short-run average total cost does not change as the quantity of output changes.
C) Long-run average total cost does not change as the quantity of output changes.
D) Long-run average total cost changes at a constant rate as the quantity of output changes.