1.I'll remember those unforgettable days when we spent together.
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答案：when→that/which或去掉when 考查定语从句的引导词。在定语从句中作宾语，所以用关系代词，作宾语也可以省略。
2．There is a large shopping centre in Wangfujing, which you can buy traditional handmade crafts like papercuts.
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答案：which→where 考查定语从句的引导词。从句中不缺少主语或宾语，用关系副词引导定语从句。先行词表示地点，故用where引导该定语从句。
