Provides a powerful and flexible security mechanism by hiding parts of the DB from certain users. The user is not aware of the existence of any attributes that are missing from the view. It permits users to access data in a way that is customized to their needs, so that the same data can be seen by different users in different ways, at the same time.
Hence Option(c)External Level data hiding is the correct choice.
Reference: http://cir.dcs.uni-pannon.hu/cikkek/Database_Environment.pdf