Final answer:
Window Concepts used the promotion mix tool of personal selling by sending representatives to a trade show to directly promote their new line of energy-efficient windows. Therefore correct option is C
Step-by-step explanation:
In the scenario where Window Concepts sends a team of representatives to the National Doors and Windows Trade Show to promote their new line of windows that offer the same benefits as solar panels, the promotion mix tool used is personal selling. Personal selling involves direct interaction with potential customers to explain the features and benefits of a product, respond to queries, and persuade them to make a purchase. This direct form of communication is particularly effective for complex products that require a detailed explanation of their advantages, as is the case with these state-of-the-art energy-efficient windows.