题目

C In ancient times, there was a king who loved flowers. His palace was always decorated with beautiful orchids(兰花) and other flowers. As the king grew older, he knew that one day he would have to give up his throne(王位). So he had to find someone to rule the country. The other day, the king had an idea. He asked his servants to travel to every part of the country and give every citizen a single orchid seed(种子). He then announced that the person who grew the most beautiful orchid would take his throne.    Everyone in the country then got their own seed. One young man named 数列{an}的通项为an=2n+1，则由bn=a1+a2+…+ann所确定的数列{bn}的前n项和是（　　）A．n（n+2）B．12n（n+4）C．12n（n+5）D．12n（n+7）