correct answer is : a-ii, b-i, c-iv, d-iii
a. Foreign keys ii. Referential integrity
b. Private key i. Domain constraint
c. Event control action model iv. Trigger
d. Data security iii. Encryption
Foreign Key : A foreign key is a column that references a column of another table. The purpose of the foreign key is to ensure referential integrity of the data.
Trigger : A trigger is a special kind of stored procedure that automatically executes when an event occurs in the database server.
Domain Constraint : refer this