SAT Question f10b7ce4: Form Structure And Sense answer and explanation

English - Form Structure And Sense - Subject Verb Agreement
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In the list “Adorable Things” from Sei Shōnagon’s Pillow Book, the author delights in baby sparrows, a face drawn on a melon, and a young courtier in ceremonial garb. So shrewd an observer is Shōnagon, a lady-in-waiting to Empress Teishi, that her book’s musings on tenth-century Japanese courtly life ______ readers a thousand years later.
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Difficulty:Hard
Which choice completes the text so that it conforms to the conventions of Standard English?