In a garbage collected environment such as .NET, how does the garbage collector specifically handle circular references between managed objects?

Introduction / Context:
Circular references occur when two or more objects reference each other, creating a cycle in the object graph. In manual memory management systems, such cycles can cause serious leaks if reference counting is used. However, .NET uses a tracing garbage collector, which is designed to cope with circular references. This question focuses on how that collector decides whether a cycle should be reclaimed.

Given Data / Assumptions:
- The runtime is the .NET common language runtime with a managed heap.
- The garbage collector uses tracing rather than pure reference counting.
- Object graphs may include complex structures with cycles.
- GC roots include stack references, static variables, and CPU registers.

Concept / Approach:
The .NET garbage collector periodically pauses managed threads and walks the object graph starting from GC roots. During this mark phase, it flags all objects that can be reached by following references from these roots. Any object not marked as reachable is considered garbage. Because the algorithm is based on reachability, not raw link counts, even cycles of objects are collectible if nothing outside the cycle points to them. The correct answer must describe this reachability based approach.

Step-by-Step Solution:
Step 1: The collector identifies all root references such as those on thread stacks and in static fields. Step 2: It recursively follows references from each root and marks every encountered object as reachable. Step 3: At the end of the traversal, any object that remains unmarked is unreachable and considered garbage. Step 4: If a group of objects reference each other but are not reachable from any root, they remain unmarked as a group and the collector reclaims them together.

Verification / Alternative check:
Practical experiments with .NET memory profilers demonstrate that objects in cycles are collected when all references from roots are removed. The documentation for the common language runtime also explains that the collector uses a graph traversal algorithm based on reachability, which inherently supports collection of cyclic structures. This confirms the explanation in the correct option.

Why Other Options Are Wrong:
Option B is wrong because it describes a limitation of naive reference counting systems, not modern tracing collectors in .NET. Option C is incorrect since the GC does not move unreachable objects to disk as a way to avoid collection. Option D is false because .NET does not forbid circular references and they do not cause compile time errors.

Common Pitfalls:
Developers sometimes worry too much about circular references and ignore more common memory issues such as event handlers and static collections that keep objects reachable. Another pitfall is assuming that disposing of an object is the same as removing all references to it. To avoid leaks, it is important to remove strong references from long lived roots rather than simply avoiding cycles.

Final Answer:
The .NET garbage collector handles circular references by marking reachable objects from GC roots and reclaiming any unmarked cycles of objects that are no longer reachable from those roots.