Why Have Social Security Numbers Traditionally Been Used as Primary

Multiple Choice

Why have Social Security numbers traditionally been used as primary keys for database tables that store personal data on individual people?

A) All other columns in such a table are functionally dependent on the Social Security number column.
B) The Social Security number is always the only candidate key in such a table.
C) A Social Security number column is functionally dependent on all the other columns in such a table.
D) The Social Security number is functionally independent of most other columns in such a table.