The abscissae and ordinates of the points a and b are the roots of the equations x² + 2ax + b = 0 and x² + 2cx + d = 0 respectively. Then the equation of the circle with ab as diameter is:
a) x² + y² - 2ax - 2by = 0
b) x² + y² + 2ax + 2by = 0
c) x² + y² - 2ax + 2by = 0
d) x² + y² + 2ax - 2by = 0