tions cods$14$h$\_02\_$ch$03\mathrm{.}04$m

Which of the following statements best defines the purpose of entity integrity?

a$.$ It validates each row will have a value identifying foreign key values in other tables.

b$.$ Lacking a primary key, it enables each row to identify other rows in other tables.

c$.$ It secures the null key in the absence of any data.

d$.$ It guarantees each entity has a unique value for the primary key and that there are no null key values.