A customer paid $1,000 in March for work to be performed in April. The company recorded a credit to Unearned Service Revenue. At the end of April, $700 of the work was completed. The adjusting entry on April 30th would:

a. not be necessary since revenue had already been recorded in March.

b. include a debit to Unearned Service Revenue and a credit to Accounts Receivable for $300.

c. include a debit to Unearned Service Revenue and a credit to Service Revenue for $700.

d. include a debit to Unearned Service Revenue and a credit to Service Revenue for $300.