问题
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2/3,1/2,3/7,7/18,() A.5/9;B.4/11;C.3/13;D.2/5
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20/9,4/3,7/9,4/9,1/4,() A、3/7;B、5/12;C、5/36;D、7
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:1,2/3,5/9,1/2,7/15,4/9,()。A.5/9 B.3/5 C.2/13D.3/7
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1/5,1/3,3/7,1/2,() A.5/9 B.1/6 C.6 D.3/5
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2/3, 1/2, 3/7, 7/18,() A.5/9 B.3/13 C.4/11 D. 2/5
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23, 9, 7, 3, 1, 3, ()。A.-5 B.-11 C.3 D.1