(1): Enable B to kill off all of A, without touching humanity, but kill off a some humans in the process. (2): Block all access between all three species, leading to a continuation of the acts of A, kill significantly less humans in the process.

I seem to recall that there was no genocide involved; B intended to alter A such that they would no longer inflict pain on their children.

The options were:

1. B modifies both A and humanity to eliminate pain; also modifies all three races to include parts of what the other races value.
2. Central star is destroyed, the crew dies; all three species continue as before.
3. Human-colonized star is destroyed; lots of humans die, humans remain as before otherwise; B is assumed to modify A as planned above to eliminate pain.