Review of the project shows that 1000 hours of the work have been finished with the fee of US$50 per hour. However, the team has finished the works with the cost of US$40,000. Schedule analysis showed that it has the records of 1200 hours. What is the project's schedule variance?
A、US$20,000
B、US$10,000
C、-US$10,000
D、-US$20,000