Difficulty: Easy
Correct Answer: Hashtable and SortedList
Explanation:
Introduction / Context:Different collections provide different access semantics. Some are key-based (associative containers), while others are position-based or bit-based. Choosing the right collection is essential for clarity and performance.
Given Data / Assumptions:
Concept / Approach:Key-based collections allow storage and retrieval by key rather than by numeric index. Hashtable provides hash-based key lookup with no ordering guarantees. SortedList stores key–value pairs sorted by keys, enabling ordered iteration and binary-search-like retrieval.
Step-by-Step Solution:
Hashtable → key-based access (e.g., ht["id"]).SortedList → key-based access plus sorted by keys.Stack → LIFO structure, no keys, push/pop/peek operations.BitArray → compact boolean store accessed by integer index, not keys.'Map' → not a .NET Framework class name in System.Collections; the closest equivalents are DictionaryVerification / Alternative check:Create a Hashtable and a SortedList and insert/retrieve items via keys; attempt the same with Stack or BitArray and observe the absence of key-based APIs.
Why Other Options Are Wrong:They include non-keyed structures or non-existent types (as named).
Common Pitfalls:Assuming Stack has named access or that BitArray supports keys beyond integer indices.
Final Answer:Hashtable and SortedList
Discussion & Comments