✅ Comprehensive and Detailed Explanation:

A (Use Data Designer in Contact Builder) is necessary because relationships must be created between data extensions in Contact Builder for Journey Builder to access and evaluate cross-data attributes.

B (Utilize Entry Data on a Decision Split) is required because Decision Splits use Entry Data or Contact Data attributes (made available via the relationships created).

❌ Why Others Are Incorrect:

C: Data Relationships in Email Studio are for segmentation and sends, not Decision Splits in Journey Builder.

D: Automation Studio updates are irrelevant to Decision Splits in real-time journey flows.

Exact Extract:

Salesforce Help: Data Designer - Contact Builder

"Use Data Designer in Contact Builder to define relationships between data extensions. These relationships allow Journey Builder to evaluate contact data across multiple extensions when using activities such as Decision Splits."

Salesforce Help: Journey Builder Decision Split

"Decision Splits evaluate attributes from the entry event data or related data extensions defined in Contact Builder."

════════════════════════════════════════════