Why was introducing foxes ineffective at quelling the rapidly-growingrabbit population

The introduction of foxes in order to control, or even decline, the rapidly growing rabbit population was not effective due to very simple reasons, reproduction rates and available area for living.

The rabbits are reproducing quicker than the foxes, and not just quicker, but in larger numbers with every lither, thus outnumbering the foxes by far, even if each fox manages to kill a rabbit or two each day.

The area available for the rabbits to live and spread out is huge, so they are not limited by a small amount of area where their number will have to stop to grow because of lack of food sources, thus spreading around without any problem, especially because of the lack of competition.

you didn't give any options but heres what i can tell you: an inference is likely to change based on additional observations. the latter is something that you have seen or sensed using your sensory organs while the former is like a conclusion out from what you have observed.