A man does not know the difficulty of anything he does it personally.A. although B. if C.

A man does not know the difficulty of anything he does it personally.
A. although
B. if
C. because
D. unless

A. although B. if C. because (答案→)D. unless解析：A. although尽管，引导让步状语从句，一般置于句首，用逗号隔开；B. if假如，尽管，是否C. because 因为，引导原因状语从句；D. unless除非，否则；句意：一个人不可能知道所有事情的难度，除非他亲自动手做它。故选D.

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