You need to design the restrictions on the Bank.Customers table. Which three actions should you perform?（）
- ADesign a trigger that verifies that the first names and surnames are not empty strings.
- BDesign a check constraint that verifies that the first names and surnames are not empty strings.
- CDesign a check constraint that uses a CLR user-defined function to verify that either the phone number is a null value or the format of the phone number is valid.
- DDesign a trigger that uses a CLR user-defined function to verify that either the phone number is a null value or the format of the phone number is valid.
- EDesign a check constraint that ensures that the phone number cannot be changed from a valid format to a null value or to an invalid format.
- FDesign a trigger that ensures that the phone number cannot be changed from a valid format to a null value.