It has to be arranger, f*ck.
If "arranger" is the a person who does musical arrangement, which, according to Wikipedia, refers either to a rewriting of a piece of existing music with additional new material or a fleshing-out of a compositional sketch
LSAC should elminate this question because 1) I got it wrong and 2) it fails to define producer and arranger and since LSAC is always supposed to give definitions of key terms (a la RC because the test doesn't require you have any "outside" working knowledge of such concepts).
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