The monthly revenue of a company is shown in millions of dollars: 2,500, 2,000, 1,500, 2,000, 2,500, 3,000, 3,000, 3,500, 2,000, 3,000, 3,500, 4,000. Find the sample variance.
a) 2,708
b) 3,000
c) 519,097
d) 566,288