句子主干是" The topic was 'The art of eating spaghetti'."。"on which"作为关系副词相当于"where",引导定语从句修饰先行词"topic"。 " The topic"→主语,"on which"→关系副词,"my eye stopped"→定从," was"→谓语," The art of eating spaghetti"→宾语。 所有的关系副词都可以转化成"介词+which"的形式,介词的选择要根据从句的意思来选择。“我的目光停留在……上”→" my eye stop on…"