The locus of the mid points of the chords of the circle `x^2+y^2+4x-6y-12=0` which subtend an angle of `pi/3`radians at its circumference is:
(A) `(x-2)^2+(y+3)^2=6.25` (B) `(x+2)^2+(y-3)^2=6.25`
(C) `(x+2)^2+(y-3)^2=18.75` (D) `(x+2)^2+(y+3)^2=18.75`