請依下文回答第 21 題至第 25 題：  For almost 60 years, the predator-prey relationship between wolves and moose on Isle Royale, asmall island in the northwest part of Lake Superior in Michigan, US, has been the focus of ongoingresearch. In recent years, however, the number of wolves on the island has  21       due to inbreeding;there now remain only two individuals—one male and one female—on the 200-square-mile island. Thishas led to  22       growth of the island’s moose herds, which graze extensively in the national park’ssurrounding forest. The situation has  23     debate about whether to attempt a genetic rescue of thewolf population or  24       any intervention and allow extinction. On September 22, the US NationalPark Service (NPS) announced its decision to  25      the wolf population. By the end of October, sixwolves from Michigan and Minnesota will be airlifted to Isle Royale by the NPS.
【題組】21
(A) multiplied
(B) swarmed
(C) dwindled
(D) softened