According to the project plan, the project should have been spent so far US$28,000, it represents US$28,000 per hour labor rate and works 1000 hours. Monitoring costs, the project manager determines that the cost performance index is 0.8. Actual project cost is US$40,000. What is the project's schedule variance?
A、–US$12,000
B、US$4,000
C、US$5,600
D、US$12,000