Save Part 1 of 4 O Points: 0 of 1 An electronic-parts manufacturer with U-shaped short-run cost curves is producing 12,000 units per month and has short-run costs as follows: ATC = $9.50, AVC = $6.50, AFC = $3.00, MC = $10.10. a. At this level of output, has the firm started experiencing diminishing marginal and average returns? How do you know? At this level of output, the firm started experiencing diminishing marginal and average returns. Diminishing marginal returns correspond to and diminishing average returns correspond to Since the firm has U-shaped cost curves and since is greater than both of these costs must be