Which programming structure allows for repeated execution of code?

The programming structure that allows for repeated execution of code is a loop. In programming, a loop is designed to execute a block of code multiple times based on a specified condition. This is useful in scenarios where you need to perform the same action repeatedly, such as iterating over a collection of items, executing a code block a certain number of times, or until a specific condition is met.

There are different types of loops, including "for" loops, "while" loops, and "do-while" loops, each of which provides flexibility in how and when the repeated execution occurs. By using loops, programmers can reduce redundancy and make their code more efficient and easier to maintain, as they avoid having to manually write the same code multiple times.

The other options are distinct programming concepts. Functions encapsulate blocks of reusable code that can be called with specific inputs and can return outputs, while classes are blueprints for creating objects and managing data and behavior in object-oriented programming. Variables store data and help manage state but do not by themselves execute any code repeatedly. Therefore, loops are the correct choice for enabling repeated execution of code.