The correct revision to sentence 6 is, "although many claims the year-round schooling has higher achievement score, the consistent studies reveal the assessments of a higher score of the nine-month calendar." Thus, option A is correct.
The revision to the sentence is given as the changes made to process the delivery of the sentence. The revision can be performed in the form of a change in the tone of the sentence, a change in the punctuation, etc.
Sentence 6 in the passage is based on the claim of a high score of year-round schooling. The sentence has to be revised in a respectful tone.
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