I regret you that we are unable to offer you a job.
A. informing
B. having informed
C. to inform
D. to informing
网友回答
A. informing
B. having informed
(答案→)C. to inform
D. to informing
解析：regret to say/inform/tell表示很遗憾……，近似于I'm sorry to say. regret doing表示对发生的事后悔，懊悔或惋惜。