Sentence that needs correction:

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> "Angela was curious about the unopened letter on the table and wondered ***for whom*** it was meant."
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I think the whom should be replaced with ***who*** because the sentence can be rewritten as 

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> Angela was curious about the unopened letter on the table and wondered "who was it meant for?"
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> 
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***Correct answer: the sentence contains no error.*** 

why am I wrong?