she will never forget the days --- she spent in beijing.

动词spent是及物动词,后边必须接宾语,但是定语从句中spent后面少了宾语,所以用关系代词which或that引导,且which在定语从句中担任spent的宾语.记住哟：关系代词which,that是可以担任成分的,而关系副词when,where,why是不能担任从句的成分的.做定语从句的题目,先看从句是否为完整的句子,如果是,就用关系副词,不是,就用关系代词.^_^