The platform gives a native tool for this situation. Use A. Fields and relationships can be created, but they will be unable to add the fields to the page layout from the canvas. The decision turns on Lightning page configuration. Lightning App Builder controls page composition, component visibility, activation, assignments, and specialized surfaces such as record pages, home pages, and utility bars.
This is how the same requirement would be handled in a well-governed Salesforce org: identify the controlling object, relationship, field, page, automation, or environment first, and then configure the native capability for that control point. The selected answer satisfies the requirement without requiring users to perform extra interpretation or administrators to maintain an unnecessary custom workaround.
The other choices would leave a gap in the implementation. B (Custom fields can be added to any custom objects, excluding formula field types.) is not enough: A formula is calculated display logic and cannot always store static values or perform record updates. C (Relationships can be made to any custom objects, but any relationships to standard objects should be built in Lightning Object Manager.) handles a different concern; A Lightning component changes the interface; it does not automatically solve security, relationship, or data-quality requirements. D ( " Save " should be clicked each time a new object, field, or relationship is create) is less defensible because it is not the most maintainable declarative control for this design. In a real org, the builder should include negative testing as well, proving that the rule does not fire or display outside the intended conditions.
---