You need to validate rows before they are added to a table every time a row is added using a user-defined function. What should you use? More than one answer may achieve the goal. Select the BEST…

While a DML Trigger (AFTER or INSTEAD OF) can also invoke a UDF for validation, it is a more complex, procedural solution and is not considered the 'best' answer when a simpler declarative CHECK constraint achieves the same goal.

A Default constraint only supplies a value for a column when no value is provided during INSERT; it does not validate or reject rows based on any condition or user-defined function.

A Foreign key constraint enforces referential integrity by ensuring a column's value exists in a referenced parent table; it does not support calling a user-defined function for custom validation logic.

A CHECK constraint can call a user-defined function to evaluate an expression and reject any INSERT (or UPDATE) that causes the expression to return FALSE or UNKNOWN, making it the ideal declarative mechanism for row validation. It fires automatically on every INSERT and UPDATE, enforcing the rule at the table level without requiring additional procedural code. This is the most direct and standard SQL Server feature designed specifically for this validation scenario.