Final answer:
First-class functions are not an aspect of the imperative style of programming; they are associated with functional programming. Imperative programming is hallmarked by assignment statements, sequential execution, and the use of variables.
Step-by-step explanation:
The aspect that is not an aspect of the imperative style of programming among the choices given is A) First-class functions. Imperative programming is characterized by a sequence of statements to determine how to reach a certain goal. It focuses on describing how a program operates. This style includes the use of B) Assignment statements, C) Sequential execution, and D) Variables. In contrast, first-class functions are a feature of functional programming paradigms, where functions are treated as first-class citizens, meaning they can be passed as arguments, returned from other functions, and assigned to variables.