Answer: d. Debit Accounts Receivable and credit Service Revenue
Step-by-step explanation:
The client is yet to pay for the service so they owe Mary. This makes them an Accounts receivable and so Mary should debit Accounts receivables to reflect this.
Mary should also credit Service revenue because the services were for work done in the current accounting period and according to the Revenue Recognition principle, have to be recognized as revenue in the period.