Which control structure is appropriate for Karel to take a ball if present, or put one down if not?

The most suitable control structure for Karel's task of taking a ball if present or putting one down if not is the If/Else statement. This structure allows for a decision-making process where there are two distinct actions based on a condition.

In this scenario, Karel needs to check whether a ball is present. The If/Else statement can effectively handle this check by:

1. Evaluating the condition: If a ball is present, Karel will execute the command to take the ball.

2. Providing an alternative action: If the ball is not present, Karel will execute the command to put a ball down.

This structure is ideal for situations where there are clear two pathways based on a binary condition (in this case, the presence or absence of a ball).

Other control structures, such as If statements, would only allow one action to occur based on the condition being true, lacking the alternative that is needed here. While loops are designed for situations where actions need to be repeated until a condition changes, which is not suitable for this specific action-oriented task. A switch statement is typically used for multi-way branching based on the value of a single variable and is more complex than necessary for this straightforward decision. Therefore, the If/Else