Let P be the point on the parabola y2=8x , which is at a minimum distance from the centre C of the circle x2+(y+6)2=1 , the equation of the circle passing through C and having its centre at P , is
a. x2+y2−4x+8y+12=0
b. x2+y2−x+4y−12=0
c. x2+y2−4x+2y−24=0
d. x2+y2−4x+9y+18=0