题目

We all know that English conversations always start with the weather. (改写句子，句意不变)     It____________ ____________ that English conversations always start with the weather. 答案：is known 【解析】我们都知道英语对话通常以天气开始。此句可改为It is known that…众所周知……。14．设Sn为数列{an}的前n项和，且a1+a2=4，$\frac{2{S}_{n+1}+1}{2{S}_{n}+1}$=$\frac{{a}_{2}}{{a}_{1}}$=c（c＞0，n∈N*）．（1）求数列{an}的通项公式；（2）令bn=anlog3an，求数列{bn}的前n项和Tn．