题目

—____inthisstreet?       —IthinkMr.Blackistherichestman.            A.Whom do you think is the richest man            B.Who do you think is the richest man            C.Do you think who is the richest man            D.Do you think whom is the richest man 答案：B等比数列{an}中，已知a1=2，a4=16（I）求数列{an}的通项公式；（Ⅱ）若a3，a5分别为等差数列{bn}的第3项和第5项，试求数列{bn}的通项公式及前n项和Sn．