Final answer:
The adjusting entry for the revenue collected in advance includes a debit to revenue of $600.
Step-by-step explanation:
The adjusting entry for the revenue collected in advance includes a debit to revenue and a credit to deferred revenue. In this case, $600 of the revenue collected in advance is earned, so the adjusting entry would include a debit to revenue of $600. The correct answer is (c) debit to revenue of $600.