题目

— It has been dry for a few months.    — You’re right. There is twice ____ rain this year than _____ of last year.    A. more; it        B. less; that         C. more; that       D. less; it 答案：B 解析: 略11．已知数列{an}的前n项和为Sn，且${a_1}=1，{S_n}=\frac{{（{n+1}）{a_n}}}{2}$，则a2017=（　　）A．2016B．2017C．4032D．4034