Concept:A trade fair is an exhibition where businesses in the same industry display and promote their products.
Explanation:A new tractor is a high-value, specialised agricultural product.
Advertising it through a trade fair allows potential buyers to see the tractor physically.
They can inspect its features, watch a demonstration, and ask direct questions.
Radio, poster, and neon sign only give general information without physical demonstration.
Therefore, a trade fair is the more suitable medium for advertising a new tractor.
Answer:D. Trade fair