Question

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Explanation:

Analyze the program goal

The program is titled "Tennis Ball Square". The goal is to have Karel place a square of tennis balls and return to his starting point.

Determine the required control structure

To draw a square, Karel needs to repeat a set of actions (placing a line of balls and turning) 4 times. This is most efficiently done using a for loop that runs 4 times:

for (var i = 0; i < 4; i++) {
    // Code to lay one side of the square
}

Identify the actions per side

For each of the 4 sides of the square, Karel needs to place tennis balls along the path and then turn left to prepare for the next side:

1. Place balls while moving forward (e.g., using a loop or a sequence of putBall(); move();).
2. Turn left at the corner: turnLeft();.

Answer:

To complete the Tennis Ball Square program, you need to program Karel to lay down four equal sides of tennis balls using a loop.

Here is the standard structure for the solution:

/* Tennis Ball Square
 * This program has Karel place a square of tennis balls
 * and return to his starting point.
 */
function start() {
    for (var i = 0; i < 4; i++) {
        putBall();
        move();
        putBall();
        move();
        putBall();
        move();
        turnLeft();
    }
}

(Note: Adjust the number of putBall(); move(); commands inside the loop depending on the exact grid size of the square required by your specific exercise level).