The endpoints of a diameter of a circle are (23,−1) and (−21,5). Which of the following is the equation of the circle in general form with integer coefficients?
a) 4x2+4y2+4x+16y−23=0
b) x2+y2−x−4y−423=0
c) 4x2+4y2−4x−16y−23=0
d) 4x2+4y2−4x−16y−143=0