SAT Question 64a40675: Boundaries answer and explanation

English - Boundaries - No Punctuation Within Clause
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In 1953, a fellow performer tripped on legendary jazz musician Dizzy Gillespie’s trumpet, bending its bell upward. When Gillespie tested the damaged instrument, he realized that he ______ sound of a bent bell over that of a straight one.
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Difficulty:Easy
Which choice completes the text so that it conforms to the conventions of Standard English?