Final answer:
The prepositional phrase in the sentence is 'in place of Mark'.
Step-by-step explanation:
The prepositional phrase in the sentence is in place of Mark. A prepositional phrase includes a preposition (in this case, in) and an object of the preposition (place of Mark). Prepositional phrases provide additional information about location, time, or manner. In this sentence, the prepositional phrase indicates that Sheila entered the writing contest on behalf of or in substitution for Mark.
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