Explanation:

The correct answer is option D - Structural level.

Data Abstraction in DBMS:
Data abstraction is a key concept in database management systems (DBMS). It refers to the process of hiding the complexities of the underlying data structures and providing a simplified view of the data to the users. In DBMS, there are three levels of data abstraction: physical level, logical level, and conceptual level.

1. Physical Level:
The physical level is the lowest level of data abstraction in a DBMS. It deals with the physical storage and organization of data on the storage media. It describes how the data is stored, accessed, and manipulated at the hardware level. This level is concerned with details such as disk storage, file structures, indexing techniques, and data retrieval algorithms. It focuses on the implementation aspects of the database system.

2. Logical Level:
The logical level is the next level of data abstraction. It describes the overall structure of the database without going into the implementation details. It defines the logical organization of data elements and the relationships between them. At this level, the focus is on the entities, attributes, and relationships between them. The logical level is also responsible for defining the integrity constraints and the operations that can be performed on the data.

3. Conceptual Level:
The conceptual level is the highest level of data abstraction in a DBMS. It provides a global view of the entire database system. It describes the overall design and structure of the database system in terms of a high-level data model, such as the entity-relationship (ER) model or the relational model. The conceptual level is concerned with defining the schema of the database, which includes the definition of entities, attributes, relationships, and constraints.

4. Structural Level:
The structural level is not a level of data abstraction in a DBMS. It is not a standard term used to describe the levels of data abstraction. It is possible that the term "structural level" is used in some specific context or in a different context outside the scope of DBMS. However, in the context of this question, the structural level is not a recognized level of data abstraction.

Conclusion:
In conclusion, the correct option is D - Structural level, as it is not a recognized level of data abstraction in a DBMS. The three recognized levels of data abstraction in a DBMS are the physical level, logical level, and conceptual level.