When help, one often says “Thank you.” or “It is kind of you “A. offeringB. to offerC. to

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A. offering
B. to offer
C. to be offered
(答案→)D. offered
解析：考查状语从句的省略式。当主从句的主语一致时，可以省略从句的主语和be动词，when offered=when one is offered….,可以用过去分词作状语，逻辑主语为one，与offer故选为被动关系，句意：当被提供帮助的时候，一个人应该说：“谢谢”或“你真好”。故选D。