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.
麻烦问下老师，我对并列这块的考点没问题，而是后面的从句that play an important...，从play分析是修饰molecules，但前句的中心词不是a biological family吗？如果修饰family，先行词得改成which,动词改成plays,即所谓的跳跃指代？that做先行词，只能修饰其紧跟着的molecules?谢谢。
