Start at the layer that controls the outcome. The best answer is C. Formula field that reached on the Account object. The selected option is not chosen because it sounds familiar; it is chosen because it gives Salesforce the right instruction at runtime. Formula and validation expressions must respect Salesforce data types.
Picklists require picklist-aware handling, dates require date functions or date arithmetic, and image or text formulas must return the correct type.
The scenario describes a business outcome, not merely an administrative preference. If the feature is configured correctly, users get the intended result without depending on memory, spreadsheets, or manual policing. That is the professional standard for Platform App Builder work: place the rule in metadata, test it under the correct permissions, and keep the design supportable.
The distractors are not equal substitutes. A (Control and Account objects: 0.00 or 1 have a Master-Detail Relationship.) handles a different concern; Master-detail is powerful, but it is wrong when the records need independent ownership or when the child-parent direction is reversed. B (Store Data: 3000 characters in the formula.) is less defensible because A formula is calculated display logic and cannot always store static values or perform record updates. D (unable to reference the child records.) would be fragile here because it could produce an inconsistent result once different users, records, or apps are tested. That is the kind of solution a Salesforce admin can document, migrate, and troubleshoot without creating hidden technical debt.
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