SAT Question 8a3998f1: Boundaries answer and explanation

English - Boundaries - Period Between Sentences
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After the United Kingdom began rolling out taxes equivalent to a few cents on single-use plastic grocery bags in 2011, plastic-bag consumption decreased by up to ninety ______ taxes are subject to what economists call the “rebound effect”: as the change became normalized, plastic-bag use started to creep back up.
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Difficulty:Easy
Which choice completes the text so that it conforms to the conventions of Standard English?