The facts already supply December performance, consumption, a customer claim, and an employee obligation; waiting for cash misstates both periods.
The December entries recognize economic activity and positions; the January entries settle the resulting asset and liability.
The cash events are new transactions, but their effects settle accounts created for the already recognized December activity rather than duplicating it.
Net income does not replace the separate customer claim, employee obligation, revenue, and expense accounts needed for reporting and settlement.
Answer: B
December performance creates $5,400 of Accounts Receivable and Service Revenue. December employee service creates $1,900 of Wages Expense and Wages Payable. Neither adjustment uses Cash. January collection debits Cash and credits Accounts Receivable; January payment debits Wages Payable and credits Cash. The same December revenue and expense are not recognized again.