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公路AB上各站之间共有90种不同的车票。
(1)公路AB上有10个车站，每两站之间都有往返车票
(2)公路AB上有9个车站，每两站之间都有往返车票
E.条件(1)和(2)单独都不充分，条件(1)和条件(2)联合起来也不充分。

A.条件(1)充分，但条件(2)不充分。
B.条件(2)充分，但条件(1)不充分。
C.条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分。
D.条件(1)充分，条件(2)也充分。

【参考答案】

A
解析：
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