Zoe's Bakery operates in a perfectly competitive industry. Suppose that when the market price is $5, the profit-maximizing output level of pastries is 150 units, with average total cost of $4, and average variable cost of $3. From this we know Zoe's marginal cost is ______, and Zoe's short-run profits are ______.
A. $5; $300.
B. $1; $300.
C. $1; $150.
D. $5; $150.