Step 1: Use the locus idea
Every point on BD is equally far from A and C, so BD is the perpendicular bisector of AC.
Step 2: Set distances equal
$(x-2)^2+(y+3)^2=(x+6)^2+(y-7)^2$. Expanding: $-4x+6y+13=12x-14y+85$, so $16x-20y+72=0$, i.e. $4x-5y+18=0$. Option (C).
Final Answer:
BD is $4x-5y+18=0$, option (C).
\[ \boxed{4x-5y+18=0} \]