Every positive number has two square roots , a principal square root and its

Definition: The square root of a number is another number, which on multiplying with itself, will give the original number.

Every positive number has two square roots. One square root is positive, while the other is exactly same, but negative. The positive square root of a number is called its principle square root. For example, 10 and -10 are the two square roots of 100, but 10 is called the principle square root. 

Hence every positive number has two square roots , a principal square root and its opposite negative.

A. is the answer in this question