Which control structure should Karel use to put down a tennis ball in a 1x1 world?

In a 1x1 world, Karel's operations are quite straightforward since there are no additional conditions or iterations needed. The most suitable control structure for Karel to put down a tennis ball in this scenario is the if statement.

Using an if statement allows Karel to check a specific condition—in this case, whether Karel is holding a tennis ball. If Karel is holding a tennis ball, the if statement can execute the command to put down the ball. This approach is efficient because it only requires a single check and corresponding action, which aligns perfectly with the simplicity of the 1x1 world. There are no loops or complex conditions required, making an if statement the ideal choice for this task.

Other control structures like a for loop or while loop are designed for repetitive actions or iterating over a sequence of steps, which are unnecessary in a world that only requires one action of putting down a tennis ball. Similarly, the switch statement is used for handling multiple possible conditions or cases, but since there are no such variations in this scenario, it is not appropriate either.