As it's a homework question here is a hint:
Imagine Ant A is stationary (it could be)...
The let's say B moves a small distance, any directionalong the line AB. How would this change distance AB?
Then, what would this mean for how distance AC has to change, and in what direction must C move - then what would that mean for what $V_C$ has to be (in terms of $V_B$)?
This seems to rule out three of the options.