Why 疑问副词作状语was 谓语the origin of life主语a sample step 表语in the Earth's history 状语把句子换成陈述句,成分会更加明了：The origin of life was a sample step in the Earth's history...那麻烦问一下这个表语是个什么用法啊a sample step 是名词作表语a sample step的核心词是step，a 和 sample都是定语修饰step