public static void Demo1()
{
     // C#2 普通调用方式
     string Log2 = ExtensionCompare.GetLogError("C#2 普通静态方式");
     Console.WriteLine(Log2);

     // C#3 扩展方法调用方式
     string Log3 = "C#3扩展方法方式".ToLogError();
     Console.WriteLine(Log3);

     Console.ReadLine();
}
/// summary>
/// C#2 常规静态方法扩展
/// /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 用扩展方法实现的string类型扩展
/// /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);