What does the term "constant returns to scale" mean on the Long-Run Average Total Cost?

A. The Long-Run Average Cost Curve is shifting up.

B. The business is operating at the low-end flat range of the Long Run Average Total Cost curve and your costs are not rising as you increase production.

C. You are getting a fixed rate of return on your financial investments.

D. The Long-Run Average Cost Curve is shifting down.