
Passage: European fern is a poisonous weed that has spread and destroyed many pastures in the northern hemisphere in recent years. A cheap and self-sustaining way to deal with this weed is to introduce the plant's natural enemies. As a result, some scientists have suggested that fern-eating moths from the southern hemisphere could be re-stocked to the northern hemisphere affected by the weed as a way to control fern growth.
Question: If the scientist's proposal to control the European fern is adopted, which of the followings is necessary for its success?
A. A.This northern hemisphere fern also grows in regions of the southern hemisphere with similar climate and soil conditions.
B. B.In addition to eating European ferns, the stocked moths also eat other weeds that grow in the northern hemisphere.
C. C.The stocked moths were able to survive in the northern hemisphere and form a group large enough to reduce the fern population and prevent its growth.
D. D.After the European fern population is reduced, livestock will develop immunity to diseases caused by this weed.
Answer: