This student managed to pass the difficult exam, ______surprised all of us.
【正确答案】 B
【答案解析】分析句子结构可知，逗号之后为非限制性定语从句，引导词在从句中作主语，指代前面整句话，所以应用关系代词which引导。that，it和what均不能引导非限制性定语从句。故选B。