6. Given points $A(-7,0), B(7,0), C(2,-12)$, if one focus of an ellipse is $C$, and the ellipse passes through points $A$ and $B$, the locus of the other focus of the ellipse is ( ).
A. Hyperbola
B. Ellipse
C. Part of an Ellipse
D. Part of a Hyperbola
6. D. Hint: Let the other focus of the ellipse be $F(x, y)$. Since $A$ and $B$ are points on the ellipse, by the definition of an ellipse, we have $|A C|+|A F|=|B C|+|B F|$, thus $|B F|-|A F|=|A C|-|B C|$. Given $|A C|=15,|B C|=13$, we get $|B F|-|A F|=2$, so the locus of point $F$ is part of a hyperbola.