When using LINQ to DataSet, you can perform aggregation operations on grouped data by using the GroupBy clause followed by the aggregation function within the Select statement. This allows you to group the data based on a specific criterion and then apply aggregate functions such as sum, count, average, etc., to each group individually. Understanding how to leverage the GroupBy clause for aggregating data is crucial for performing complex data analysis tasks using LINQ to DataSet.

A DataView is indeed a subset of a DataTable. It represents a specific view of the data, allowing you to filter and sort its contents according to your requirements.

The System.Linq namespace in C# includes the Queryable class, which provides methods for querying data sources that implement IQueryable. It enables building dynamic LINQ queries and supports composition of query operations. Therefore, the correct option is "Queryable."

Data binding in the Repeater and DataList controls differs from other data controls in that it does not have built-in support for automatically generating its content based on the data source. Instead, it provides greater flexibility by allowing developers to customize the HTML markup for each item. This approach gives more control over the presentation of data but requires more manual coding compared to controls like GridView or DataGrid.

Code First approach in Entity Framework allows developers to define entity classes in code and then generate a database schema from those classes. This approach is particularly useful when starting a new project or when the database schema can be derived from the application's domain model.

DataRelations in ADO.NET maintain relationships between related tables, facilitating navigation and querying of hierarchical data structures such as parent-child relationships.

A DataAdapter serves as a bridge between a DataSet and a database connection. It helps in transferring data between the DataSet and the data source, facilitating data retrieval and manipulation.

Language-Integrated Query (LINQ) is a set of features introduced in .NET Framework that allows for querying data from different data sources using a unified syntax. In the context of ADO.NET Entity Framework, LINQ provides a way to query entities using familiar C# or VB.NET syntax, making it easier to work with database data in an object-oriented manner.

The correct option is "Eager Loading". In LINQ to Entities, eager loading is used to fetch related data along with the main query to reduce the number of database round-trips. It retrieves the main entity as well as its related entities in a single query, which can improve performance by reducing the amount of data retrieved from the database. Eager loading helps in optimizing queries and reducing the overhead of lazy loading or multiple round-trips to the database.

The LINQ to Entities query syntax resembles Declarative SQL. It allows developers to write queries in a way that is similar to SQL, focusing on what data should be retrieved rather than how.