Which statement is true?

You issue the following command to alter the country column in the departments table:

Which statement is true?

A.
It produces an error because column definitions cannot be altered to add default values.

B.
It executes successfully and all the rows that have a null value for the country column will
be updated with the value ‘USA’.

C.
It executes successfully. The modification to add the default value takes effect only from
subsequent insertions to the table.

D.
It produces an error because the data type for the column is not specified.