Deferred execution in LINQ means that the query is not executed until the results are requested or enumerated. This allows for more flexibility and optimization in querying large datasets or databases. Thus, the correct option is "Enumerated."

The data reader is connected to the database until you explicitly call the Close() method. Calling this method releases the resources associated with the data reader and closes the underlying database connection, preventing unnecessary resource consumption and ensuring proper cleanup.

The DataView class in ADO.NET is commonly employed for advanced data binding tasks. It allows for flexible sorting, filtering, and searching of data within a DataTable, making it suitable for various data presentation needs.

In the Code-First approach of Entity Framework, to update data, you retrieve the entity from the database, modify its properties, and then call the SaveChanges() method on the context to persist the changes to the database. The framework handles tracking changes and generating the necessary SQL statements to update the database.

ADO.NET Entity Framework abstracts the database schema, allowing developers to interact with conceptual entities rather than dealing directly with database tables and columns. This abstraction simplifies data access and makes the application more maintainable and adaptable to changes in the underlying database structure.

The primary difference between Code-First and Database-First approaches in Entity Framework lies in how the database schema and application's data model are created. In Code-First, developers define the application's data model using classes, and the database schema is then generated based on these classes. In contrast, Database-First starts with an existing database schema, from which Entity Framework generates the application's data model as classes. This fundamental distinction affects the development workflow and the way developers interact with the database during application development.

CRUD stands for Create, Read, Update, Delete. It represents the four basic functions of persistent storage, commonly used in database management systems. Create involves adding new records, Read involves retrieving existing records, Update involves modifying existing records, and Delete involves removing records from the dataset.

The SqlConnection class in ADO.NET is responsible for managing the connection pool. It provides methods for opening, closing, and managing connections to a SQL Server database. When connection pooling is enabled, SqlConnection automatically manages the pooling of database connections, optimizing the performance of database interactions in .NET applications.

The main difference between IEnumerable and IQueryable in LINQ lies in their execution behavior. IEnumerable is suitable for querying in-memory collections where execution happens on the client side. IQueryable, on the other hand, is used for querying databases where execution occurs on the server side. IQueryable allows for composing LINQ queries and executing them remotely, while IEnumerable supports deferred execution but lacks this remote execution capability.

When using a DataAdapter to fill a DataSet, the commonly used SQL statement is SELECT. This statement is used to retrieve data from a database based on specified criteria. It allows you to fetch data from one or more tables, apply filters, and define the order of results. By executing a SELECT statement, the DataAdapter retrieves the requested data and fills it into the DataSet for further manipulation and analysis within the application.