The Short-Run Supply Curve of a Perfectly Competitive Firm Is

The short-run supply curve of a perfectly competitive firm is the

A) upward-sloping portion of its average total cost curve
B) upward-sloping portion of its average variable cost curve
C) average fixed cost curve at all levels of output
D) marginal cost curve, which lies above the average variable cost curve
E) downward-sloping portion of its marginal cost curve