Tangents `OA and OB` are drawn from the origin to the circle `(x-1)^2 + (y-1)^2 = 1`. Then the equation of the circumcircle of the triangle `OAB` is : `(A) x^2 + y^2 + 2x + 2y = 0` (B) `x^2 + y^2 + x + y = 0` (C) `x^2 + y^2 - x - y = 0` `(D) x^2+ y^2 - 2x - 2y = 0`