Overgrazing by rabbits is harming agriculture.
Plan is to introduce a virus that will reduce rabbit population.
There is a small chance that the virus will infect bilby (native wildlife) too.

Conclusion: Plan may help agriculture but will clearly INCREASE threat to native wildlife.

Our conclusion says that the threat to native wildlife will increase because of the introduction of virus. So whatever is the threat to native wildlife right now, it will increase by the introduction of the virus. What is our assumption here?


A) There is less chance that the virus will infect domestic animals on Tambor than that it will infect wild animals of species native to the island.
Irrelevant. Comparison with domestic animals are out of scope. We are talking about wildlife only.

B) Overgrazing by rabbits does not pose the most significant current threat to the bilby.
Correct. We are concluding that threat will increase. What if overgrazing is a huge threat right now which could affect the bilby population badly? Then introducing the virus may actually reduce the threat - after all, there is a small chance that the virus will affect bilby. Introducing the virus will eliminate the overgrazing threat and introduce a small chance that the virus could affect bilby. So it is possible that introducing the virus may decrease the overall threat to wildlife.

C) There is at least one alternative means of reducing the rabbit population that would not involve any threat to the bilby.
Irrelevant. We are discussing the merits/demerits of this plan.

D) There are no species of animals on the island that prey on the rabbits.
If there are some species that prey on the rabbit, introducing the virus may reduce their food supply. So the wildlife may suffer. Hence our conclusion becomes stronger, if anything.

E) The virus that the government proposes to use has been successfully used elsewhere to control populations of rabbits.
We don't know and it doesn't matter. The virus has caused epidemic in rabbit population and that's all.

Answer (B)