Merge fields are placeholders used within Salesforce prompt templates to dynamically insert data from specific records. When a prompt template is executed on a record, such as a Case, the merge fields are replaced with the actual data from that record's fields (e.g., Case Number, Subject, Description). This allows the administrator to create a single template that generates a customized, context-aware summary for any given customer case, directly fulfilling the requirement to populate the response with real Salesforce data.

A. Flow: A Flow is an automation tool for processes. While it can retrieve data, it is not the syntax used within the prompt template itself to display record field values.

B. Picklists: Picklists are a type of field that provides a list of predefined values. They are a source of data, not the mechanism for inserting that data into a template.

C. Agent Instructions: Agent Instructions are directives for the Large Language Model (LLM) on how to process the prompt and data, but they are not the feature used to pull the record data in.

1. Salesforce Help Documentation, "Prompt Template Builder": Under the section for creating the prompt template content, the documentation states, "To add context from Salesforce records, use merge fields. For example, to add a case subject, enter {!$Record.Subject}." This directly confirms that merge fields are the designated tool for this purpose.

2. Salesforce Trailhead, "Prompt Fundamentals" Module, "Create a Prompt Template" Unit: This module explains, "To ground the prompt in your Salesforce data, you can add merge fields for any object. When a user runs the prompt, the merge fields are populated with data from the record that the user is on." This reinforces the use of merge fields for dynamic data population from records.

3. Salesforce Developers Documentation, "Prompt Template Pilot": In the guide for creating prompt templates, it specifies the use of merge fields to reference record data. For example, "Use merge fields to ground the prompt in CRM data. For example, {!$Record.Name}." This provides a developer-level confirmation of the feature's function.