D, irrational numbers. The opposite of squaring something is to find the square root and the square root of 20 is 4.4... 4.4 is an irrational number, therefore that is your answer. It wouldn't be rational because you can t write it as a fraction, 4.4 isn't a whole number so its not natural, and its not an integer because if you have anything right of the decimal point that is not zero, it's not an integer.