SAT Question 96953201: Boundaries answer and explanation

English - Boundaries - No Punctuation Within Clause
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In her two major series “Memory Test” and “Autobiography,” painter Howardena Pindell explored themes ______ healing, self-discovery, and memory by cutting and sewing back together pieces of canvas and inserting personal artifacts, such as postcards, into some of the paintings.
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Difficulty:Easy
Which choice completes the text so that it conforms to the conventions of Standard English?