I think it is your thesis
To my mind the correct answer is (A).
"Many Americans travel to Costa Rica during the winter months, the peak season, because of the warmer temperatures found at many of Costa Rica’s tropical beaches and lush rain forests. "
In this sentence, the author decides to add additional information through an APPOSITIVE PHRASE. If the writer decides to delete "the peak season" from the sentence, the meaning of the sentence will remain.
Plentiful.
Hope this helps!
Helping verbs<span> are </span>verbs<span> that, as their name suggests, help the main </span>verb<span> in a sentence by extending the meaning of the </span>verb<span>. They add detail to how time is conveyed in a sentence. As a result, </span>helping verbs<span> are used to create the most complicated </span>verb<span> tenses in English: the progressive and the perfect aspects.
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