C

When Prompt Builder accesses related list data through an object like Account, the available fields are determined by what the current user can see — and that visibility is driven by:

field-level security and
the default page layout assigned to that user

Wrong options
A. Use field picker after selecting related list
Field picker only shows what is already visible — it doesn't determine visibility

B. Assign fields as JSON
Prompt Builder does not require JSON formatting to access related list fields

Amar Option A. After selecting a related list from the Account, use the field picker to choose merge fields in Prompt Builder.

C is the correct answer

C is the correct answer

I will change my answer since I found this in trailhead couple days ago

The correct answer is
A. After selecting a related list from the Account, use the field picker to choose merge fields in Prompt Builder.

Explanation
When you add a related list (like Contacts, Cases, or Opportunities) as a grounding resource in a prompt template, you don't get all fields from all related records.

The correct procedure is to first select the related list you want to use. After that, Prompt Builder will present a field picker. The Agentforce specialist must then use this picker to explicitly select the specific fields (merge fields) from that related list that they want to be included in the prompt.

B. JSON Format: You don't need to manually format the fields as JSON. Prompt Builder handles the formatting behind the scenes after you select the fields.

C. Page Layout: The fields available are not determined by the user's page layout. This is a common point of confusion. The fields must be explicitly selected within the Prompt Builder interface itself, independent of the UI layout....

c is the answer

C is the correct answer

When using a standard Related List Merge Field in Prompt Builder to ground a prompt, the system automatically gathers a snapshot of that related data.

Data Source Rule: The specific fields included in the snapshot for the related records (e.g., fields from the Contacts or Opportunities related to the Account) are determined by the fields displayed on the Page Layout of the parent object (Account) that the current user (the user running the Agent/Prompt) has assigned to them.

Limitation: This means if an important field is not on the user's assigned Account page layout's related list section, that field will not be available for the AI to use in the prompt, regardless of whether it exists on the record.
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Why the Other Options are Incorrect
A. After selecting a related list from the Account, use the field picker to choose merge fields in Prompt Builder. This is partially true for selecting the related list, but the available fields are restricted by the page layout (Option C). More importantly, this option describes the action of selecting, not the consideration/rule governing which fields are available, which is the core concern of the auditing team.

B. Prompt Builder must be used to assign the fields from the related list as a JSON format. Prompt Builder automatically converts the related list data into a structured format (like JSON) when inserting it into the prompt for the LLM. The Specialist does not manually assign the format; the platform handles it. Manual JSON formatting is typically reserved for complex scenarios using Apex or Flows....

C is the correct answer

C is correct answer