A law firm consists of five partners: Alice, Bob, Carol, Dave, and Ellen. If Ellen is on a case, then Bob is not. If Bob is on a case, then Carol is not. If Carol is on a case, then Dave is. If Dave is on a case, then Alice is not. If Alice is on a case, then Ellen is not.<br> If only one partner can be on the case, who must it be?
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A
Alice
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B
Bob
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C
Carol
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D
Dave
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E
Ellen