题目

When asked how a statue from distant Greece ________ have appeared in China, researchers explained that ________ this was a result of Alexander the Great's influence. A . should; no wonder B . could; no doubt C . might; no need D . would; no rush 答案：B已知各项均为正数的数列{an}满足a1=1，an+1+an•an+1-an=0．（Ⅰ）求证：数列是等差数列，并求数列{an}的通项公式；（Ⅱ）求数列前n项和Sn．