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. (The use of "chair" as a gender-neutral term instead of "chairman" may be contested.)
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The postman needs to know who this letter is addressed to so it can be delivered. (The phrase "who this letter is addressed to" is often regarded as an example of informal or nonstandard usage; it could be contested in more formal contexts.)