题目

I should very much like to have gone to the party but I _________.    A．am not invited               B．am not being invited C．shall not be invited    D．was not invited 答案：D 解析: 由should like to have gone可知是对过去事实的谈论，我本想去的，但未被邀请。故选D。2．已知正项数列{an}的前n项和Sn满足2$\sqrt{{S}_{n}}$=an+1，求证：{an}是等差数列，并求an．