Which of the following expressions is always non-negative for all real xxx?
x2−2x+1x^2 - 2x + 1x2−2x+1
x2−2x−1x^2 - 2x - 1x2−2x−1
−x2+2x−1-x^2 + 2x - 1−x2+2x−1
x3+1x^3 + 1x3+1