John said he’d been working in the office for an hour, ________ was true．

John said he’d been working in the office for an hour, ________ was true．

答案C
该非限制性定语从句缺少主语，A、B两项不能用作关系代词，D项只能指代人，而该从句需要关系代词指代主句所说的事实，用which。