What is the primary use of LINQ in programming?

LINQ, which stands for Language-Integrated Query, is primarily used for data querying within various data sources in a unified and simple manner. It allows developers to write queries directly in their programming language, making the process of data retrieval more intuitive and integrated with the programming constructs.

When using LINQ, you can query collections, databases, XML documents, and other data sources using a similar syntax, regardless of where the data resides. This integration means that much of the complexity traditionally associated with querying different data types is simplified. It provides a consistent model to work with, leveraging strong typing and compile-time checks, which significantly reduces errors compared to string-based queries.

In contrast, options such as file handling, database connectivity, and user interface design address different aspects of application development. While LINQ can be used in conjunction with databases (making it useful for database connectivity), its core strength lies in the querying aspect. Thus, its primary use is indeed in data querying, allowing for efficient and readable manipulation of data across various formats and sources.