—Amy,I called you yesterday evening,but nobody answered the phone. —Oh,I a walk with my mother at that time. [ ]
A.
take
B.
took
C.
am taking
D.
was taking
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【简答题】(Ⅰ)已知公差不为0的等差数列{a n }的首项a 1 =1,前n项和为S n ,若数列 是等差数列, ①求a n ; ②令 (a>0),若对一切n∈N*,都有 ,求q的取值范围; (Ⅱ)是否存在各项都是的无穷数列{c n },使 对一切n∈N*都成立?若存在,请写出数列{c n }的一个通项公式;若不存在,说明理由。