单项选择题
A.23 B.37 C.46 D.43
A.2 B.1 C.0 D.-1
A.acbed B.decab C.deabc D.cedba
A.n1+n2+...+nm B.(m-1)nm+...+n2+1 C.n1+n2+1 D.n1-n2
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