Since it is an argumentative editorial, the correct answer to which revision would most improve sentence 7 (It is about time that we replaced our outdated and inefficient school calendars) is the revision upon the presence of the first person in its plural form, expressed by the pronoun "we".
An <em>argumentative essay</em> has as characteristic <em>a neutral tone</em>. It consists of a <em>text written in the third person, and not in the first person</em>, which would bring a personal tone to the text. The pronoun <em>"we"</em> gives the reader the impression that the speaker is <em>representing a specific group of people</em> with his speech, and not providing an <em>argumentative opinion based on facts and data</em>. The <em>third person</em> conveys an <em>objective opinion based on arguments</em>, and not a <em>personal opinion that can cause mistrust on the reader</em> because it can imply a lack of knowledge.
Therefore, <em>the revision that would most improve sentence 7 is the replacement of the first person "we"</em>, in the sentence, by the third person, which would give<em> a neutral tone to the argumentative editorial</em>.