public static void Demo1()
{
     // C#2 普通調用方式
     string Log2 = ExtensionCompare.GetLogError("C#2 普通靜態方式");
     Console.WriteLine(Log2);

     // C#3 擴展方法調用方式
     string Log3 = "C#3擴展方法方式".ToLogError();
     Console.WriteLine(Log3);

     Console.ReadLine();
}
/// summary>
/// C#2 常規靜態方法擴展
/// /summary>
/// param name="loginfo">格式化信息/param>
/// returns>/returns>
public static string GetLogError(string loginfo)
{
     return string.Format("This is C#2 style: {0}", loginfo);
}
/// summary>
/// C#3 用擴展方法實現的string類型擴展
/// /summary>
/// param name="loginfo">/param>
/// returns>/returns>
public static string ToLogError(this string loginfo)
{
     return string.Format("This is C#3 style: {0}", loginfo);
}

company.Department.Select
(dept => new
{
     Name = dept.name,
     Cost = dept.Employees.Sum(person=>person.Salary);
})
.OrderByDescending(x=>x.Cost);