Concept:For a real square root, the expression inside it must be non-negative, and the denominator must never be zero.Explanation:We require 1+xx≥0 and 1+x=0.The critical points are x=−1 and x=0.For x<−1, both x and 1+x are negative, so 1+xx>0. Hence (−∞,−1) is included.At x=−1, the denominator becomes zero, so this point is excluded.For −1<x<0, the fraction is negative, so this interval is rejected.At x=0, 1+00=0≥0, so 0 is included.For x>0, both are positive, so 1+xx>0 and (0,∞) is included.Combining the valid intervals, the domain is (−∞,−1)∪[0,∞).Answer:(−∞,−1)∪[0,∞)Hence, the correct option is A.