asp.net季度问题

//本季度第一天
      DateTime firstMonth = DateTime.Now.AddMonths(0 - ((DateTime.Now.Month - 1) % 3));
      startTime = Convert.ToDateTime(firstMonth.ToString("yyyy-MM-01"));
//本季度最后一天
　　endTime = startTime.AddMonths(3).AddSeconds(-1);
 　 //endTime = startTime.AddMonths(3 - ((DateTime.Now.Month - 1) % 3)).AddDays(-1);