You are a database developer. You plan to design a database solution byusing SQL Server 2008. You are creating adataba seto support the office manager. Your  database  model has the  following  structure.

The database design has the following business requirements: An employee can be assigned more than one  task. Upon completion, thetask is deleted. When a task is deleted, the associated assignment is deleted. When an employee is nolonger available tocomple tea task, theemployee link to the assignment is replaced with a NULL value. You need to implement the business requirements to maintain data integrity.
What should you do?（）

A.Create DDL INSERT triggers on the Employee. Task and  Assignment entities.
B.Create CHECK constraints on the Task  ID and Employee  ID attributes in the  Assignment entity.
C.Create  Foreign  Keys constraints on  the  Task  ID and  EmployeeID attributes in the  Assignment entity. Reference the Task and  Employee entities respectively. Specify the  appropriate On Delete action.
D.Create  Foreign  Keys constraints  on  the  Task  ID and  Employee  ID attributes in theTask and  Employeeentities respectively. Reference the  Assignment entity, and specify the  appropriate On Delete action.