分析句子,并指出主干:
In an English class是时间状语, students是主语 from all the contries from the east是介词短语作定语,修饰主语, were required是被动语态作谓语动词,to introduce some of their places of interest是动词不定式短语作主语补足语, that are world-famous是定语从句,修饰places of interest.
主干: In an English class, students were required to introduce some of their places of interest