The Long-Run Average Cost Curve Is U-Shaped Because of Which

Multiple Choice

The long-run average cost curve is U-shaped because of which of the following?

A) Constant fixed costs as output is increased.
B) Decreasing average fixed costs as output is increased.
C) Economies and diseconomies of scale.
D) Decreasing marginal returns as more labour is hired.
E) Increasing marginal returns as more labour is hired.