* A validation rule can ensure that theLead Sourcefield is populated before the Lead is converted. This prevents users from proceeding unless the required data is entered.
Why not other options?
* A: Triggers are programmatic, whereas a declarative solution like validation rules is simpler and more efficient.
* B: Lead Conversion field mapping maps fields between Lead and Account/Contact but cannot enforce field requirements.
* C: A formula field is read-only and cannot enforce user input.
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Validation Rules Documentation