I took the liberty to correct your typing. The original question does not have the verb "is" after the word "brother". The way you typed it, none of the options would be correct. The proper question is this one:
<em>Which sentence is punctuated correctly?
</em>
<em>A) My brother a truck driver, spends a great deal of time on the road. </em>
<em>B) My brother, a truck driver spends a great deal of time on the road. </em>
<em>C) My brother, a truck driver, spends a great deal of time on the road. </em>
<em>D) My brother, a truck, driver spends a great deal of time on the road.</em>
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The sentence that is punctuated correctly is option C) My brother, a truck driver, spends a great deal of time on the road. The structure "a truck driver" is an appositive. That means its function in this sentence is to give further information or an explanation about something that was just mentioned - in this case, the word brother. The speaker is explaining that his/her brother spends a lot of time on the road because he is a truck driver. Appositives should come between commas. That's why option C is the right one.
