Which of the following is not a Python built-in data type?

• A. list
• B. dictionary
• C. array
• D. set

Answer: (C)

In Python, built-in data types include lists, dictionaries, and sets, which are fundamental structures used to store and manipulate collections of data. A list is an ordered collection of items that can be changed, a dictionary is a collection of key-value pairs that allows for fast lookups, and a set is an unordered collection of unique items.

On the other hand, the term "array" does not refer to a built-in data type in Python. While Python does have a module called array that provides an array data structure, it is not a foundational type in the same sense as lists, dictionaries, and sets, which are readily available in the language without needing to import any additional modules. Therefore, in the context of built-in data types directly supported by Python, "array" is the correct answer as it does not belong to the core set of data types provided by the language.