* A: Formula fields are calculated at runtime based on the formula definition and are not stored in the database.
* C: Formula fields can reference fields from related objects, allowing cross-object calculations.
Why not other options?
* B: Formulas cannot reference themselves; doing so would result in a circular reference error.
* D: If a field used in a formula field is deleted, the formula field will break, and Salesforce will prevent deletion until the formula field is updated.
References:
* Formula Fields Documentation