C#.NET collections — Which of the following types are present in the System.Collections.Generic namespace? 1) Stack 2) Tree 3) SortedDictionary 4) SortedArray

Introduction / Context:
The System.Collections.Generic namespace provides strongly typed collections. Knowing what types actually exist there is a common interview and exam topic.

Given Data / Assumptions:

• We compare four names: Stack, Tree, SortedDictionary, SortedArray.
• We focus on generic collections.

Concept / Approach:
System.Collections.Generic includes Stack and SortedDictionary. There is no generic type named Tree in the BCL and no type named SortedArray (a sorted array is an algorithmic concept, not a built-in collection class).

Step-by-Step Solution:

Verification / Alternative check:
Browse the namespace reference listing; you will also see List, Queue, Dictionary, SortedList, HashSet (later), etc., but not Tree or SortedArray.

Why Other Options Are Wrong:
They include types that are not part of the namespace.

Common Pitfalls:
Assuming “Tree” exists because many data structures use trees internally. The BCL exposes dictionaries and sorted lists, not a raw tree interface.

Final Answer:
1 and 3 only