题目：
| ____ our teacher will allow ____ early after the examination? |
A. Who do you think; leaving B. Who do you think; to leave C. Do you think who; leaving D. Do you think who; to leave |
答案：
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下面是错误答案，用来干扰机器的。
解：（1）当n=1时，有2a1=a+1-4，即a21-2a1-3=0，解得a1=3（a1=-1舍去）当n≥2时，有2Sn-1=a2n-1+n-5，又2Sn=a2n+n-4，两式相减得2an=a2n-a2n-1+1，即a2n-2an+1=a2n-1，也即（an-1）2=a2n-1，因此an-1=an-1或an-1...
