SAT Question e35d481c: Words In Context answer and explanation

English - Words In Context - Fill In Blank Single Word
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Some economic historians ______ that late nineteenth- and early twentieth-century households in the United States experienced an economy of scale when it came to food purchases—they assumed that large households spent less on food per person than did small households. Economist Trevon Logan showed, however, that a close look at the available data disproves this supposition.
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Difficulty:Hard
Which choice completes the text with the most logical and precise word or phrase?