It seems to me that, the thing wthat <span>the author has done in order to create a tone of seriousness in this piece is </span>a fact that he has used a long sentence with complex syntax to ask the reader to pay close attention.
Even though you haven't shared any options to choose the correct one, I bet this one will suit the question.
Regards.
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Allowance is to motivate a child to help around the house.
This is an example of a linking verb
