InsertOnSubmit method is used to insert a new record into a LINQ to SQL data context. It queues the object to be inserted upon calling the SubmitChanges method. This method is specifically designed for adding new records. The Add method is not part of LINQ to SQL; it's typically used with Entity Framework. Update is used to modify existing records, and Attach is used to attach existing objects to a data context, not for inserting new records.

ADO.NET provides classes such as OleDbCommand for OLE DB providers and SqlCommand for SQL Server providers, allowing developers to create parameterized queries specific to different database providers.

The correct option is "Entities". In LINQ to Entities, the Entity Framework maps database tables to entity classes, where each entity class represents a table in the database. These entities are used to perform operations such as querying, updating, and deleting data in the underlying database. The term "Entities" refers to these classes that are used to represent the database tables in LINQ to Entities.

Excessive use of the Include method can result in fetching unnecessary data, leading to performance degradation. Ignoring database schema and relationships can lead to inefficient query execution. Parameterized queries prevent SQL injection attacks and optimize query execution. Overusing LINQ-to-Entities can result in inefficient translation of LINQ queries to SQL, impacting performance.

The correct answer is "Text." The DataTextField property is used to specify the field from the data source that will be displayed as the text in the DropDownList control. For instance, if your data source has a "Name" field, you would set DataTextField to "Name" to display names in the DropDownList.

The WHERE clause is used to filter rows returned by the SELECT statement based on a specified condition. It allows you to specify a condition that must be met for each row to be included in the result set. This condition can include comparisons, logical operators, and functions, allowing for flexible filtering of data.

Stored procedures are beneficial when the application requires complex business logic to be executed on the database side. They offer advantages such as improved performance, enhanced security, and encapsulation of business logic within the database. By using stored procedures as command objects in ADO.NET, developers can centralize and manage database logic efficiently, promoting maintainability and scalability in the application architecture.

Eager loading in LINQ to Entities preloads related entities along with the main entity to reduce additional database queries. This can significantly improve performance by minimizing the number of round trips to the database. Understanding when to use eager loading versus lazy loading is crucial for optimizing performance in LINQ to Entities.

In .NET, the IsDBNull method is used to check for NULL values in a data reader. This method is available on data reader objects such as SqlDataReader, OracleDataReader, and others. It returns true if the specified column contains a NULL value, allowing developers to handle NULL values appropriately in their applications. Using IsDBNull ensures data integrity and prevents errors when processing query results that may contain NULL values.

The correct option is JOIN. The JOIN clause is crucial for retrieving data from multiple related tables in a single SQL query. It allows you to combine rows from two or more tables based on a related column between them. Using JOINs helps in avoiding multiple queries and improves query performance.