Which function will teach Karel how to spin in a circle one time?

The correct function to teach Karel how to spin in a circle one time is defined in option C. This function, named spin, calls the turnLeft() command four times in succession. When Karel turns left four times, it effectively makes a complete 360-degree turn and ends up facing the same direction from which it started.

This is a fundamental aspect of Karel’s movements; each turnLeft() adjusts Karel's direction by 90 degrees to the left. Therefore, with four turns, Karel completes a full rotation, which aligns perfectly with the requirement of spinning in a circle one time.

Other options either do not complete a full circle or serve different functions. For instance, the function in option A would turn Karel around 180 degrees, which does not constitute a full circle. Option B, while it also completes a spin, is unnecessarily verbose as it performs the same action as option C but without the intended naming or clarity. Lastly, option D only involves a single left turn, which would simply change Karel's facing direction without achieving a complete spin.