When the price faced by a firm in a competitive market was $5, the firm produced nothing in the short run. However, when the price rose to $10, the firm produced 100 tons of output. From this we can infer that
the firm's marginal cost curve must be flat.
the firm's marginal cost of production never falls below $5.
the firm's average total cost of production was less than $10.
the minimum value of the firm's average variable cost lies between $5 and $10.