If a Firm Experiences Constant Returns to Scale Throughout

If a firm experiences constant returns to scale throughout:

A) the long run average total cost curve is a negatively sloped curve.
B) the short run average total cost curves are tangential to the long run average total cost curve at a point on their positively sloped portion.
C) the short run average total cost curves are tangential to the long run average total cost curve at their minimum points.
D) the short run average total cost curves are tangential to the long run average total cost curve at a point on their negatively sloped portion.
E) the long run average total cost falls to zero.