According to a company's unadjusted trial balance at Dec. 31, the balance in the Uneari. Revenue account was $400. 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 debit Service Revenue, $100: credit Unearned Revenue, 5100 O debit Unearned Revenue, $100; credit Service Revenue, $100 O debit Service Revenue $300: credit Unearned Revenue $300 debit Unearned Revenue, $300; credit Service Revenue $300