12. (5 分) 数列 $\left\{a_{n}\right\}$ 满足 $a_{n+1}+(-1){ }^{n} a_{n}=2 n-1$, 则 $\left\{a_{n}\right\}$ 的前 60 项和为 ( )
Gaokao · Math · previous-year question
- A.3690
- B.3660
- C.1845
- D.1830
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