Which of the following statements is true about primary keys? aThe function of the primary key is to guarantee entity integrity, not to describe" the entity b$.$ The function of the primary key is to guarantee entity integrity, and to "describe" the entity primary key is the attribute or combination of attributes that uniquely identifies entity instances in an entity set. $.$ A primary key is the attribute or combination of attributes that identifies entity instances in an entity set e$.$ A and C f$.$ A and D g and D