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考查强调句型和主语从句。it is _____ a man thinks of himself …      really determines his fate．是一个强调句型，第二空填that；去掉it is。。。that后，剩下_____ a man thinks of himself really determines his fate，而_____ a man thinks of himself是句子作主语，是主语从句，且这个从句缺少of的宾语，要用what。所以选C。