Researchers now regard interferon as not a single substance, but it is rather a biological family of complex molecules that play an important, though not entirely defined, role in the immune system.
as not a single substance, but it is rather a biological family of complex molecules that play
as not a single substance but as a biological family of complex molecules playing
not as a single substance but as a biological family of complex molecules that play
not to be a single substance but rather a biological family of complex molecules playing
not as a single substance but instead as being a biological family of complex molecules that play
选 C 而不是B 因为that 这个从句修饰了molecules
登录 或 注册 后可以参加讨论