Which data structure is the default standard for general-purpose database indexes (e.g., CREATE INDEX in MySQL/Postgres)?

1. A Hash Map, which offers constant-time O(1) lookups but cannot handle range queries or order-by operations.
2. B Skip List, a probabilistic data structure that provides logarithmic search time and is commonly used in in-memory databases.
3. C B-Tree (Balanced Tree), which maintains sorted order and is optimized for the block-based storage architecture of physical disks.
4. D Linked List, a fundamental linear structure that stores data in discrete nodes and requires a full scan for every search operation.