In C sharp, what is the purpose of the reserved word using when it is used in normal code, not in documentation?

Introduction / Context:
The reserved word using in C sharp serves two important roles. It appears at the top of files to simplify type names by importing namespaces, and it appears in using statements that manage the lifetime of disposable resources such as file handles and database connections. This question tests whether you understand both purposes of the keyword in real code.

Given Data / Assumptions:
- The language is C sharp in the .NET environment.
- Namespaces group related types and must be referenced to use their names.
- Some resources implement IDisposable and require deterministic cleanup.
- The keyword using can appear in two syntactic forms.

Concept / Approach:
At the top of a C sharp file, using System; imports the System namespace, which allows code to refer to Console instead of System.Console. Inside method bodies, using can start a using statement that ensures Dispose is called on an object at the end of the scope, even if an exception occurs. The correct answer must mention both the namespace import and the scoped disposal behavior, which are the two standard uses.

Step-by-Step Solution:
Step 1: Recall that using directives simplify type names by importing namespaces. Step 2: Remember that using statements are written as using (var resource = new SomeDisposable()) { ... }. Step 3: Understand that when control leaves the using block, the compiler generates code to call Dispose on the resource. Step 4: Select the option that correctly describes both namespace import and automatic cleanup of disposable resources.

Verification / Alternative check:
If you remove a using directive at the top of a file, you may need to fully qualify type names, which proves that the directive controls namespace imports. When you rewrite a using block as explicit try finally code that calls Dispose, you see that the compiler translates the using statement into structured cleanup logic. Documentation and examples confirm both of these roles.

Why Other Options Are Wrong:
Option B is wrong because using does not control unmanaged compilation; compilation always produces managed code for C sharp unless special interop is used. Option C is incorrect since using does not create global variables. Option D is false because using clearly affects how the compiler resolves names and generates resource cleanup code, so it is more than a comment marker.

Common Pitfalls:
A common pitfall is forgetting to wrap disposable resources in using blocks, which can delay cleanup and exhaust handles or connections. Another issue is confusing using directives with project references; removing a using directive does not remove the actual assembly reference. Good practice is to add using directives only for namespaces actually used and to use using statements consistently for IDisposable resources.

Final Answer:
In C sharp, the reserved word using is used to import namespaces so that type names are easier to reference and, in using statements, to define a scope where IDisposable objects are automatically disposed at the end of the block.