Which control structure would be best to have Karel put down 300 tennis balls?

Using a for loop is the most efficient control structure for having Karel put down 300 tennis balls because it allows you to specify a clear starting point, an end condition, and an increment, all in one concise statement. This is particularly useful in scenarios where the number of iterations is known beforehand, such as putting down a set number of items.

In this case, a for loop can be set up to iterate exactly 300 times, directing Karel to perform the action of putting down a tennis ball on each iteration. This not only keeps the code clean and easy to read, but it also minimizes potential errors by managing the counting and looping in a structured manner.

While a while loop could also accomplish the task, it would require additional setup to ensure that Karel puts down the correct number of tennis balls, as it generally checks a condition before each iteration. If the condition is not properly managed, it could lead to errors in the number of balls placed. The other options, such as an if statement and a switch statement, do not fit this context well. An if statement is used for conditional branching rather than repeated actions, and a switch statement is not designed for iterative processes; it is best suited for selecting among multiple cases without looping.