The correct answer is: A. do-while
A do-while loop always processes its instructions at least once, even if the condition is false. This is because the condition is checked at the end of the loop, not at the beginning. This means that the instructions in the loop will always be executed at least once, before the condition is checked.
A for loop is similar to a do-while loop, but the condition is checked at the beginning of the loop. This means that if the condition is false at the beginning, the instructions in the loop will never be executed.
A while loop is also similar to a do-while loop, but the condition is checked at the beginning of the loop. However, unlike a do-while loop, a while loop will not execute the instructions in the loop if the condition is false at the beginning.
Therefore, the only loop that always processes its instructions at least once is a do-while loop.