Final answer:
To record the cost of supplies used during the year and prepare the adjusting entry at December 31 in accounting, debit the Supplies Expense account and credit the Supplies account.
Step-by-step explanation:
The question pertains to accounting and the specific task is to record the cost of supplies used during the year and prepare the adjusting entry needed at December 31.
An adjusting entry is required at the end of the accounting period to ensure accurate financial statements. To record the cost of supplies used during the year, we would debit the Supplies Expense account and credit the Supplies account. The adjusting entry on December 31 would involve debiting Supplies Expense and crediting Supplies.