For a natural monopoly firm, the resource-allocative efficient output is 200 units. The highest per-unit price that can be charged for this output is $3. Average total cost at 200 units is $3.50. For the natural monopoly firm that produces and sells 200 units of output,

a.it takes losses of $1.50 per unit.b.fixed costs must be zero.c.marginal cost is below its average total cost.d.variable costs must be zero.