The two sentences that contain an example of contested usage are:
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The chair for the chair of the board of directors is at the head of the board table. (Here, "chair" can refer to different meanings, such as the person leading the board (chairperson) or the physical chair itself, leading to contested usage.)
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The postman needs to know who this letter is addressed to so it can be delivered. (In this sentence, "who" in the phrase "who this letter is addressed to" is debated; some grammarians argue that it should be "whom" in formal usage.)
These examples illustrate how language can be interpreted differently based on context and grammatical standards.