题目

—Is there ____ in your exercise book today?       —No, Mom. I did it very carefully.         A. something wrong            B. wrong something         C. anything wrong              D. wrong anything 答案：C已知数列{an}是等差数列，a2=6，a5=18，数列{bn}的前n项和为Tn，且．（Ⅰ）求数列{an}的通项公式及其前n项和Mn；（Ⅱ）求证数列{bn}是等比数列，并求出其通项公式与前n项和Tn公式；（III）记cn=an•bn，求数列{cn}的前n项和Sn．