The best answer is D because the requirement combines two constraints: the OmniScript must be embedded on a third-party website and it must be prefilled using URL-passed data. An Experience Cloud page can host the OmniScript, and the third-party website can embed that page in an iFrame while passing URL parameters.
Salesforce documentation confirms that OmniScript URL parameters can prefill fields and must use the c__ prefix in URL query-string format. Option A describes the parameter style, but by itself it does not explain how the OmniScript is embedded on the third-party website. Option C is the standard off-platform LWC
/OmniOut-style idea, but the question specifically emphasizes URL-based prefill, which fits the Experience Cloud/iFrame pattern more directly.

The developer must configure the Cache Key Property so cached data is separated by customer-specific input, such as AccountId. Without a cache key tied to the customer, cached Integration Procedure output can become too broad and potentially return the same cached response across different customers. Cache Duration only controls how long the cached value remains valid; it does not define which input makes one cache entry different from another. Response JSON Path controls what part of the response is returned, not how cache entries are partitioned. Cache Clear Key is related to clearing cached content, not creating customer-specific cache entries. Salesforce's Integration Procedure caching guidance confirms that caching improves performance but must be configured correctly for the data context.

Margin controls spacing outside an element, so Margin Bottom is the correct property when the goal is to create or reduce space between the Text element and the Button below it. Padding controls internal spacing inside the boundaries of the selected element; it would move the text within its own box rather than primarily controlling the gap between two separate elements. Layout controls structural placement and responsiveness, not direct vertical spacing. Spacer can be used as a separate layout object, but it is not the property on the Text element itself. Salesforce's FlexCard styling guidance separates dimensions, spacing, classes, and inline styles, and the spacing-around-element documentation specifically uses margin controls for external spacing.

Integration Procedure is the correct tool because the requirement goes beyond a simple Salesforce record extraction. Complex filtering, sorting, aggregation, orchestration, and preparation should be handled server- side before the OmniScript displays the result. A Data Mapper Extract is appropriate for retrieving Salesforce data, but it is not the best orchestration layer when multiple operations and preparation logic are required. An HTTP Action only calls an external endpoint; it does not by itself manage the full data-preparation workflow.
A Set Values Action is useful for assigning values in the OmniScript data JSON, not for complex server-side data shaping. Salesforce describes Integration Procedures as server-side processes used to automate data operations between Salesforce and external systems, which matches this requirement.

According to the OmniStudio Developer Guide, "To upsert a record, select the Upsert Key checkbox for the field that contains the unique identifier for the record. If you want to create a new record when no match is found, select Is Required for Upsert." Therefore, the correct answer is B.