Which control structure is guaranteed to run only one time?

The control structure that is guaranteed to run only one time is the single execution block. A single execution block is designed to execute its content exactly once during a program's flow, making it suitable for tasks that require initialization or a single-instance action. This characteristic distinguishes it from other options.

Loops, for instance, are intended to execute a block of code multiple times based on certain conditions. Functions can be called multiple times throughout a program, potentially leading to numerous executions of the same code. Conditional statements, although they can lead to a single execution in certain circumstances, depend on specific conditions being met and can be bypassed entirely.

Thus, the single execution block is uniquely identified by its one-time execution principle, making it an essential programming concept for tasks that do not require repetition.