题目

Though a week’s military training （军训）was hard, ________ they loved it.     A. or              B. so                     C. but                   D. / 答案：D在公差不为零的等差数列{}中，，成等比数列.（1）求数列{}的通项公式；（2）设数列{}的前项和为，记.求数列的前项和.