The time I first spend with Nelson Mandela was a very difficult period of my life.Awhe

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A. when
(答案→)B. which
C. of which
D. at which
解析：句意：我第一次和曼德拉度过的时光是我生命中非常困难的一段时期。这个句子包含一个定语从句，且关系词在从句中作宾语，指物，故用关系代词 which，选B。