To simplify users' interactions with the system, developers hide the complexity of system, database through several levels of abstraction: The Physical level describes how the data are actually stored, the Database System hides this level of detail from database programmers,（ ） may be aware of certain details of the physical organization of the data; The abstraction level of abstraction exists to simplify their interaction with the system; Logical level describes what data are organized in the database.

A Application

B Application

C Database administrators

D Naive users