Final answer:
The complete adverb clause in the sentence is 'so that you can prepare for the final.'
Step-by-step explanation:
The complete adverb clause in the sentence 'So that you can prepare for the final, let's meet in the library to study' is 'so that you can prepare for the final.' This adverb clause functions to explain the purpose or reason for meeting in the library to study. It provides information about why the action of meeting and studying is being done.
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