Nature reserves are very important for preserving many animals and plants, which would run the risk of being extinct.
A. otherwise
B. therefore
C. though
D. instead
网友回答
(答案→)A. otherwise
B. therefore
C. though
D. instead
解析：A否则，要不然；B因此；C然而；D代替，而不是；句意：对于保护很多野生动植物来说自然保护很重要，要不是这些动植物会有灭绝的危险。根据句意说明A项符合上下文。