Treat the requirement as something users will depend on daily. The proper configuration is C. Text field; D.
Number field. In Salesforce terms, this is a data import and matching issue. Salesforce import tools differ by data volume, matching logic, and operation. Data Import Wizard is guided and duplicate-aware for supported objects; Data Loader is stronger for larger updates, upserts, and clearing values.
The selected configuration is the professional answer because it is native, declarative, and placed at the right scope. If the requirement later expands, another administrator can inspect the same metadata area and understand how the behavior is being produced. That is far better than a solution that depends on hidden assumptions or user training.
The rejected choices solve different problems. A (Phone field) is less defensible because it is not the most maintainable declarative control for this design. B (URL field) should be rejected because it works at the wrong scope for the object, field, page, automation, or deployment condition in the stem. The configuration remains understandable for future admins because the decision is visible in metadata rather than buried in a workaround.
For imports, the builder should choose the tool based on record count, supported object, operation type, duplicate handling, and the presence of an external identifier.
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