C#获取指定日期为一年中的第几周

/// <summary>
/// 获取指定日期，在为一年中为第几周
/// </summary>
/// <param name="dt">指定时间</param>
/// <reutrn>返回第几周</reutrn>
private static int GetWeekOfYear(DateTime dt)
{
GregorianCalendar gc = new GregorianCalendar();
int weekOfYear = gc.GetWeekOfYear(dt,CalendarWeekRule.FirstDay, DayOfWeek.Monday);
return weekOfYear;
}