In Karel challenges, what is typically used to indicate a successful completion?

The indication of successful completion in Karel challenges is primarily demonstrated through the completion of all designated tasks. This means that Karel successfully navigated through the environment and performed all actions required to solve the challenge, which may include picking up beepers, moving to certain locations, or executing specific commands. When Karel finishes all assigned tasks, it signifies that the challenge is complete and has been executed as intended.

The other options do not signify successful completion as clearly. For instance, the number of beepers left could vary based on the tasks Karel was instructed to do, and it does not directly reflect whether the challenge was completed successfully. An error message indicates some form of failure or issue in the execution, signaling that Karel did not complete the challenge as required. Movement speed is related to how efficiently Karel operates but does not determine success; it is more of a variable related to Karel's execution of tasks. Thus, the completion of all designated tasks is the definitive measure of successful performance in Karel challenges.