Your company assigns three possible credit ratings to customers: Poor, Good, andExcellent (represented numerically by 1,

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Your company assigns three possible credit ratings to customers: Poor, Good, andExcellent (represented numerically by 1, 2, and 3). The DBA has just added a RATING column to the CUSTOMERS table and has asked you to add an item to your form so that credit ratings can be recorded.To restrict data entry clerks to one of these three values, you decide to create a radio group for the Rating item.You want to allow for an undetermined (Null) credit rating, and users should be able to update the credit rating from a value to an undetermined rating. How can you implement this?

A. Create three radio buttons for each of the credit ratings, and set the Mapping of Other Values for the radio group to Null.
B. Create three radio buttons for each of the credit ratings, and set the Mapping of Other Values for the radio group to one of the credit rating values.
C. Create four radio buttons, and leave blank the value for the undetermined credit rating.
D. Choose a different type of input item, because radio groups do not allow entry and update of null values.