A Short-Run Average Total Cost Curve Will Touch the Long-Run

Multiple Choice

A short-run average total cost curve will touch the long-run average cost curve at a level of output only

A) where the short-run cost curve is downward sloping.
B) where the short-run cost curve is upward sloping.
C) when the quantity of the fixed factor being employed is at the optimal level for that level of output.
D) where the short-run cost curve is downward-sloping and the quantity of the fixed factor is optimal.
E) by coincidence.