题目

The traffic police were searching for evidence to prove the accused man's________but in vain. A．mistake                       B．guilt C．fault                         D．defect 答案：B已知数列{an}的前n项和为Sn，且2Sn=n2+n（n∈N*）．（I）求数列{an}的通项公式；（II）求证：．