Consider the family of all circles whose centers lie on the straight line y = x. If this family of circles is represented by the differential equation Py"+ Qy' + 1 = 0, where P, Q are functions of x, y and dy dx y' (here y' = = ", y": d y -), then which of the following statements is (are) true ? dx (A) P = y + x (C) P+Q=1-x+y+y' + (y) (B) P=y-x (D) P-Q=x+y-y' - (y)