By definition, the square root of a squared number must be non-negative. If x is positive, √x² = x. If x is negative, say -3, √(-3)² = √9 = 3 (which is -x). This behavior precisely matches the definition of the modulus function |x|. Option B is wrong because it fails for negative x. Option C is a common misconception; a function must return a unique value, not two values. Option D is wrong for positive x.