Mercury Company sells tickets in advance for its weekly productions and records the proceeds as Unearned Revenue. At the end of each month, the company makes an adjusting entry to account for the tickets used during the month (ticket revenue.) On March 1, the Unearned Revenue account had a credit balance of $6,000, representing 300 tickets at $20 each. During March, Mercury sold an additional 500 tickets at $20 each, and 450 tickets were used during the month. What is the balance in Unearned Revenue at the end of March? ..... A. debit balance of $6,000 B. credit balance of $7,000 C. debit balance of $7,000 O D. credit balance of $6,000