A list consists of last names, first names, address and pin codes if all people in the list have the same last and the same pin code, a useful key would be A. The pin code B. The last name C. A compound key consisting of the first name and the last name D. All of the above

The correct answer is C. A compound key consisting of the first name and the last name.

A key is a column or set of columns in a table that uniquely identifies each

row in the table. In this case, the last name and the pin code are not unique, because all people in the list have the same last name and the same pin code. Therefore, a compound key consisting of the first name and the last name is the only option that would be a useful key.

A compound key is a key that consists of two or more columns. A compound key is necessary when a single column is not enough to uniquely identify each row in a table. In this case, the last name and the pin code are not unique, because all people in the list have the same last name and the same pin code. Therefore, a compound key consisting of the first name and the last name is the only option that would be a useful key.