Recursive problems are implemented by

- Queues: Queues follow the First-In-First-Out (FIFO) principle, which does not naturally support the recursive call stack model. - Stacks: Stacks follow the LIFO principle, making them suitable for implementing recursion. Each recursive call can be thought of as pushing a new layer onto the stack. - Linked Lists: While linked lists can be used to implement stacks or queues, they themselves are not directly used to implement recursion in the way stacks are. - Strings: Strings are not directly related to the implementation of recursive algorithms. Given the nature of recursion and the need for a LIFO data structure to manage the call stack, stacks are the most directly relevant to implementing recursive problems.