—Yes. My grandfather was one of them. He went there in his .
A:1990s; twenties
B:1990s; twenty
C:the 1990s; twentieth
D:the 1990s: twenties
阅读下面的材料,根据要求修改。(不得改变原意)
有个戏,写国民党统治时期,两位小学教师谈话。一个说:“看这群孩子多可怜,个个面如菜色!”老舍先生认为可以改得更通俗些;又说,假如把这句话再改一下,不仅让观众听得懂,还会引导他们去想,就更有力量了。
已知数列{an}是无穷等比数列,其前n项和是Sn,若a2+a3=2,a3+a4=1,则limn→∞Sn的值为____ .