SAT Question 2bb7416a: Boundaries answer and explanation

English - Boundaries - Period Between Sentences
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In paleontology, the term “Elvis taxon” gets applied to a newly identified living species that was once presumed to be extinct. Like an Elvis impersonator who might bear a striking resemblance to the late musical icon Elvis Presley himself, an Elvis taxon is not the real thing, ______ is a misidentified look-alike.
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Difficulty:Hard
Which choice completes the text so that it conforms to the conventions of Standard English?