Final answer:
The central selling point should be the most persuasive piece of information that aids the prospect in making a buying decision, effectively presented in a way that highlights the product's unique benefits and value proposition.
Step-by-step explanation:
The central selling point in a sales communication, such as a sales letter, should be the item of information that will help the prospect the most in reaching a decision to buy (a). This is because the central selling point effectively encapsulates the unique value proposition and primary benefits of the product or service being offered. It is the compelling reason for the prospect to consider the purchase. While the central selling point could also relate to the value compared to the cost (b), it is not specifically constrained to the last paragraph of your sales letter (c) nor the first sentence (d), though it should be made clear early in the communication. It's critical to develop paragraphs around the main point, providing sufficient evidence and examples that reinforce and elucidate the central selling point to the reader.
Effective sales letters should also introduce the central idea in a topic sentence at or near the beginning of the paragraph. This sets the stage for the evidence and analysis that follow, which support the selling proposition. Emphasizing the point toward the end of the paragraph or communication can also help to engrave the selling message in the prospect's mind. The combination of a strong central selling point with supportive details can persuade the audience analytically, leading them to engage with the offer on the merits of the product or service's features and benefits.