You can never imagine what great trouble I have had______ the customer to withdraw a claim.
【正确答案】
C
【答案解析】此题容易根据had误选过去分词persuaded。解题关键在于识别固定短语have troubledoing sth.“做某事有困难”,what great trouble I have是一个感叹句结构,将其转化成正常结构,即I have had great trouble in doing...,所以答案为C。