Final answer:
The sentence that correctly uses commas is: My boss, who happens to be my brother-in-law, let me take the day off.
Step-by-step explanation:
The sentence that correctly uses commas is:
My boss, who happens to be my brother-in-law, let me take the day off.
In this sentence, the commas are used correctly to set off the nonessential clause 'who happens to be my brother-in-law'. This clause provides additional information but is not necessary for the main meaning of the sentence.
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