L
That kind of thing was done a few times in history to get rid of various pests (use a predator to cull the pest), and unfortunately it always ends up as an even greater ecological problem (the predator overpopulates and starts becoming a pest, just larger), which I suspect is why they aren't doing it...
right
Australia being a painful case in point with several disastrous introductions and a few accidental ones
if I'm not mistaken, I think Hawaii also had some bad intros