The main topic of discussion is the product Increment, which is the sum of all the Product Backlog items completed during a Sprint and the value of the increments of all previous Sprints1. The product Increment is demonstrated and inspected by the attendees, and feedback is collected to inform the next Sprint Planning12. The Sprint Review may also include other topics, such as the Product Backlog, the Product Goal, the market conditions, the budget, and the timeline, but the product Increment is the essential topic1234. The Scrum process, and how it was used during the Sprint, is not a topic for the Sprint Review, but rather for the Sprint Retrospective, which is a separate event where the Scrum Team inspects and adapts its way of working1. Coding and engineering practices are also not relevant for the Sprint Review, as they are internal aspects of the Development Team that do not affect the value of the product Increment1. Therefore, the correct answer is C. The product Increment.