What is the correct answer with explantion please

On December 30 of the current year, KPMG signs a $150,000 contract to provide accounting services to one of its clients in the next year. KPMG has a December 31 year-end. Which accounting principle or assumption requires KPMG to record the accounting services revenue from this client in the next year and not in the current year? a. Business entity assumption b. Revenue recognition principle c. Monetary unit assumption d. Cost principle e. Going-concern assumption