How can Karel be instructed to pick beepers until none are left?

The most effective way to instruct Karel to pick beepers until none are left is to use a while loop with the hasBeeper() condition. This approach is ideal because a while loop continues to execute as long as the specified condition is true. In this case, the condition checks whether Karel has a beeper to pick up.

By structuring the command this way, Karel will repeatedly perform the action of picking up the beeper until it encounters a point where there are no more beepers left. The loop continuously evaluates the hasBeeper() condition, ensuring that Karel will only stop executing the pick action when all beepers have been collected.

The other options do not provide this flexibility. A repeat loop is generally suitable for a known number of iterations rather than an indefinite process based on a condition. A for loop requires a predetermined number of iterations and does not adapt dynamically to the presence of beepers. Defining a recursive function, while a valid programming approach, introduces unnecessary complexity for this specific task, where a simple looping construct suffices. Thus, utilizing a while loop is the most straightforward method to effectively achieve the goal of picking all beepers.