A.
B, C, E and F are automatically ruled out. The number under a square root sign can never be negative.
D is incorrect because 0 is included. When x = 0, the square root of 0 is 0. And of course 0 is less than one.
So A is correct. Any number between 0 and 1 is less than or equal to 1, and not negative (which is impossible)
