Final answer:
The correct main clause of the sentence is 'Since the football team was good this year, the homecoming game was sold out.'
Step-by-step explanation:
The entire main clause in the sentence is: Since the football team was good this year, the homecoming game was sold out.
The main clause contains the subject 'the homecoming game' and the predicate 'was sold out'. It expresses a complete thought and can stand alone as a sentence.
In this sentence, 'Since the football team was good this year' is a subordinate clause that provides additional information but is not a complete thought on its own.
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