Which of the following is an accurate statement about the envelope relationship?
a) At the planned output level, short-run average total cost equals long-run average cost, but at all other output levels, short-run average total cost is lower than long-run average cost.
b) At the planned output level, short-run average total cost equals long-run average cost, but at all other output levels, short-run average total cost is higher than long-run average cost.
c) The long-run average cost curve touches the minimum point of each short-run average total cost curve.
d) The long-run average cost curve is identical to the lowest short-run average cost curve.
