Which programming language data type consists of single-value units?

The choice of simple data type is correct because it defines a category of data that consists of single-value units, which are indivisible and represent one specific piece of data. Examples of simple data types include integers, floats, characters, and booleans. Each of these data types is designed to hold a single value, making them fundamental building blocks in programming.

In contrast, complex data types, composite data types, and abstract data types involve multiple values or a more complex structure. Complex data types typically combine simple data types to create more sophisticated units, while composite data types (like arrays or records) gather multiple values together in a structured format for organization and manipulation. Abstract data types are defined by the operations that can be performed on them rather than their concrete implementation, often encapsulating multiple values or behaviors. Therefore, the definition and use of simple data types clearly distinguish them as single-value units, making this choice the most appropriate answer to the question.