The gentleman ________ you told me yesterday proved to be a thief．
A.whoB.about whomC.whomD.with whom在线课程B
解析：
搭配“tell sb．about/of sb．/sth．(向某人讲有关某人/某事)”中的sb．在定语从句中由关系代词whom代替，介词about/of可提前。