Answer:
The correct answer is letter "C": To do well on final exams, students should not only study every day but also get enough sleep.
Step-by-step explanation:
Parallel structures are sentences that follow the same pattern of verbs, adjectives, or nouns providing each of them the same level of importance. The statements are connected with a coordinating conjunction that could be: "for", "and", "nor", "or", "but", "so", or "yet".
In the example:
A) To do well on final exams, students should not only study every day but also be getting enough sleep. (Different verb structures)
B) To do well on final exams, students should not only have studied every day but also sleep enough. (Different verb structures)
C) To do well on final exams, students should not only study every day but also get enough sleep. (Parallel verb structures)