Final answer:
The marginal cost curve for the oil refinery is comprised of three line segments with different marginal costs at different production levels.
Step-by-step explanation:
The marginal cost curve for the oil refinery can be represented by three line segments. The first segment, MC Segment 1, has a marginal cost of 0.001q until a production level of 4,000 barrels. The second segment, MC Segment 2, has a constant marginal cost of 4 between 4,000 and 6,000 barrels. The third segment, MC Segment 3, has a marginal cost of 4+0.002(q-6,000) from 6,000 to 10,000 barrels.
Using this information, you can draw the marginal cost curve for the refinery by connecting the three line segments on the graph.