Which of the following is a mutable data type in Python?

• A. tuple
• B. string
• C. set
• D. list

Answer: (D)

In Python, a mutable data type is one that allows its elements to be changed after it has been created. Lists fall under this category. They can store a collection of items, and you can alter this collection by adding, removing, or modifying elements without creating a new list. For instance, you can append new items, remove existing ones, or change the value of an item at a specified index.

On the other hand, tuples and strings are immutable. This means that once they are created, their contents cannot be changed. For tuples, you cannot add or remove items; similarly, with strings, you cannot modify characters directly. Sets, while being mutable, allow for the addition and removal of items, but lists specifically allow for indexed access and repeated items, making them a fundamental and widely used mutable type in Python.

Thus, the choice indicating lists truly represents a mutable data type within the context of Python programming.