Choose the correct relative pronoun: The automaton, ______ was designed by the boy's father, became the key to understanding their relationship.
答案解析
核心考点：非限制性定语从句引导词 解题思路：逗号后的非限制性从句必须用which引导 选项分析：B正确（which引导非限制性定语从句）；A错误（that不能用于非限制性从句）；C错误（whom指代人）；D错误（where表地点） 易错点：混淆限制性与非限制性定语从句的区别
正确答案：B