题目

A couple of weeks ago, a few friends and I had an opportunity to attend a dear friend’s wedding in New York. After the wedding and reception, rather accidentally four of us gathered in a hotel room and began to explore the deeper meaning of life and death. What does it mean to live truly? If we are all getting closer to death, is all the material accumulation worth it? It is not exactly the type of conversations one has at a wedding. While the answers varied from person to person, I was left with more questions than answers and a feeling of gratefulness to be surrounded by friends who数列{an}中，n≥2，且an=an-1-2，其前n项和是Sn，则有（　　）A．nan＜Sn＜na1B．na1＜Sn＜nanC．Sn≥na1D．Sn≤nan