According to a company's unadjusted trial balance at Dec. 31, the balance in the Unearned Revenue account was $800. This balance represents receipt of four months of service received on December 1 from a customer. The monthly contract service to be provided is for the months of Dec., Jan., Feb. and March. The required adjusting entry for Dec. 31 would be

a.	debit Unearned Revenue, $200; credit Service Revenue, $200

b.	debit Service Revenue, $200; credit Unearned Revenue, $200

c.	debit Unearned Revenue, $600; credit Service Revenue, $600

d.	debit Service Revenue, $600; credit Unearned Revenue, $600