Misunderstandings resulting from lack of social communication, if not properly, may lead

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A. handling
B. being handled
(答案→)C. handled
D. to handle
解析：考查if引导的条件状语从句的省略。If引导的条件状语从句，如果从句主语和主句主语一致，且含有be动词，这时可以把从句的主语和be动词省略。补充完整应是if misunderstandings are not handled properly,所以选C。