According to The Elements of Style, Which Answer Choice Is Consistent With Strunk's Rules?

The answer

"Omit needless words" is the single most quoted principle in The Elements of Style. Strunk stated it as Rule 17 and elaborated: "Vigorous writing is concise. A sentence should contain no unnecessary words, a paragraph no unnecessary sentences, for the same reason that a drawing should have no unnecessary lines and a machine no unnecessary parts." So any answer choice that says to revise your writing to cut out needless words is directly consistent with Strunk.

Crucially, "omit needless words" does not mean writing must be short or stripped of detail. Strunk explicitly said it "requires not that the writer make all his sentences short, or that he avoid all detail... but that every word tell." Conciseness is about eliminating deadwood (phrases like "the fact that," "in a hasty manner," "there is no doubt but that"), not about starving sentences of meaning.

Why the other options are wrong

"Discard the passive voice entirely." Strunk's Rule 11 is "Use the active voice," and he did favor it as "more direct and vigorous." But he never said to abolish passive voice. He gave clear cases where the passive is the correct, natural choice, for example "The dramatists of the Restoration are little esteemed today," where the subject under discussion is the dramatists, not who esteems them. A rule to eliminate passive voice completely misstates his more nuanced guidance.

"Avoid the Oxford (serial) comma." This is the opposite of what Strunk taught. His Rule 2 is "In a series of three or more terms with a single conjunction, use a comma after each term except the last." That is a direct endorsement of the serial comma ("red, white, and blue"). Choosing to avoid it contradicts the book.

"Write short sentences with little detail." As noted above, Strunk specifically rejected this reading of his own conciseness rule. Brevity for its own sake, at the cost of detail and clarity, is not what he advocated. Every word should tell, but the sentence should still say what it needs to say.

The bigger picture

The Elements of Style began as a slim 1918 handbook by William Strunk Jr., his Cornell students' "little book." It was later revised and expanded by his former student E. B. White in 1959, which is why it is universally called "Strunk and White." The book's enduring rules cluster around a few ideas: prefer the active voice, be concise, be specific and concrete, and follow standard punctuation such as the serial comma. When a multiple-choice question asks which option is "consistent with Strunk," the safest bet is almost always the one that echoes clarity and concision, because that is the spine of the entire book.