Which statement about a stack data structure is true?

• A. It follows First-In-First-Out.
• B. It stores data in no particular order.
• C. It allows random access to elements by index.
• D. It follows Last-In-First-Out order.

Answer: (D)

Stacks operate on a Last-In-First-Out principle. You add items with push and remove them with pop, so the most recently added element is the first one to come off. That predictable order is what makes this data structure distinct from a queue, which would remove items in the order they arrived (First-In-First-Out). Stacks also don’t support random access by index; the top element is the only one you can access directly, so you can’t efficiently reach elements buried beneath without popping off the ones above. For example, if you push A, then B, then C, popping will yield C first, then B, then A. This behavior is precisely what the statement about a stack being Last-In-First-Out describes.