Rock Consulting was hired by Fiona Company on December 1 to hire and train a new executive team. Fiona Company paid $3,500 to Rock Consulting for services to be provided over the next seven months. Rock Consulting recorded the entire $3,500 as revenue upon receipt of the cash. As of December 31, Rock Consulting has completed one month of the consulting services. What adjusting entry would Rock Consulting make on December 31